I have this same issue but I already have NuGet setup and selected. I followed your instructions nevertheless but I still get the same results. 
Any advice?
my error are mostly NU1605, CS0006, NU1903 etc. All of them are marked “Warning As Error” but I have 69 of them and I get 6 Packages that failed to build
5>C:\Users\xbox.nuget\packages\microsoft.extensions.dependencyinjection.abstractions\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.DependencyInjection.Abstractions.targets(4,5): warning : Microsoft.Extensions.DependencyInjection.Abstractions 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
5>C:\Users\xbox.nuget\packages\microsoft.extensions.options\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Options.targets(4,5): warning : Microsoft.Extensions.Options 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
5>C:\Users\xbox.nuget\packages\microsoft.extensions.configuration.abstractions\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Configuration.Abstractions.targets(4,5): warning : Microsoft.Extensions.Configuration.Abstractions 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
5>C:\Users\xbox.nuget\packages\microsoft.extensions.options.configurationextensions\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Options.ConfigurationExtensions.targets(4,5): warning : Microsoft.Extensions.Options.ConfigurationExtensions 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
5>C:\Users\xbox.nuget\packages\microsoft.extensions.logging.abstractions\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Logging.Abstractions.targets(4,5): warning : Microsoft.Extensions.Logging.Abstractions 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
5>C:\Users\xbox.nuget\packages\microsoft.extensions.dependencyinjection\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.DependencyInjection.targets(4,5): warning : Microsoft.Extensions.DependencyInjection 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
5>C:\Users\xbox.nuget\packages\microsoft.extensions.logging\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Logging.targets(4,5): warning : Microsoft.Extensions.Logging 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
5>C:\Users\xbox.nuget\packages\microsoft.extensions.configuration\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Configuration.targets(4,5): warning : Microsoft.Extensions.Configuration 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
5>C:\Users\xbox.nuget\packages\microsoft.extensions.logging.configuration\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Logging.Configuration.targets(4,5): warning : Microsoft.Extensions.Logging.Configuration 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
5>C:\Users\xbox.nuget\packages\microsoft.extensions.logging.console\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Logging.Console.targets(4,5): warning : Microsoft.Extensions.Logging.Console 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
5>C:\Users\xbox.nuget\packages\microsoft.extensions.http\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Http.targets(4,5): warning : Microsoft.Extensions.Http 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
5>CSC : error CS0006: Metadata file ‘D:\Epic Games\UE_5.4\Engine\Source\Programs\Shared\EpicGames.Build\bin\Development\net6.0\ref\EpicGames.Build.dll’ could not be found
5>CSC : error CS0006: Metadata file ‘D:\Epic Games\UE_5.4\Engine\Source\Programs\Shared\EpicGames.IoHash\obj\Development\net6.0\ref\EpicGames.IoHash.dll’ could not be found
5>Done building project “EpicGames.UHT.csproj” – FAILED.
6>------ Build started: Project: UnrealBuildTool, Configuration: Development Any CPU ------
6>C:\Users\xbox.nuget\packages\system.diagnostics.diagnosticsource\9.0.0\buildTransitive\netcoreapp2.0\System.Diagnostics.DiagnosticSource.targets(4,5): warning : System.Diagnostics.DiagnosticSource 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
6>C:\Users\xbox.nuget\packages\microsoft.extensions.primitives\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Primitives.targets(4,5): warning : Microsoft.Extensions.Primitives 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
6>C:\Users\xbox.nuget\packages\microsoft.extensions.dependencyinjection.abstractions\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.DependencyInjection.Abstractions.targets(4,5): warning : Microsoft.Extensions.DependencyInjection.Abstractions 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
6>C:\Users\xbox.nuget\packages\microsoft.extensions.options\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Options.targets(4,5): warning : Microsoft.Extensions.Options 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
6>C:\Users\xbox.nuget\packages\microsoft.extensions.configuration.abstractions\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Configuration.Abstractions.targets(4,5): warning : Microsoft.Extensions.Configuration.Abstractions 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
6>C:\Users\xbox.nuget\packages\microsoft.extensions.logging.abstractions\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Logging.Abstractions.targets(4,5): warning : Microsoft.Extensions.Logging.Abstractions 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
6>C:\Users\xbox.nuget\packages\microsoft.extensions.dependencyinjection\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.DependencyInjection.targets(4,5): warning : Microsoft.Extensions.DependencyInjection 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
6>C:\Users\xbox.nuget\packages\microsoft.extensions.logging\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Logging.targets(4,5): warning : Microsoft.Extensions.Logging 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
6>C:\Users\xbox.nuget\packages\microsoft.extensions.configuration\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Configuration.targets(4,5): warning : Microsoft.Extensions.Configuration 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
6>C:\Users\xbox.nuget\packages\microsoft.extensions.http\9.0.0\buildTransitive\netcoreapp2.0\Microsoft.Extensions.Http.targets(4,5): warning : Microsoft.Extensions.Http 9.0.0 doesn’t support net6.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set true in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.
6>D:\Epic Games\UE_5.4\Engine\Source\Programs\UnrealBuildTool\UnrealBuildTool.csproj : warning NU1903: Package ‘Microsoft.Extensions.Caching.Memory’ 6.0.1 has a known high severity vulnerability, Microsoft Security Advisory CVE-2024-43483 | .NET Denial of Service Vulnerability · CVE-2024-43483 · GitHub Advisory Database · GitHub
6>D:\Epic Games\UE_5.4\Engine\Source\Programs\UnrealBuildTool\UnrealBuildTool.csproj : warning NU1903: Package ‘System.Net.Http’ 4.3.0 has a known high severity vulnerability, .NET Core Information Disclosure · CVE-2018-8292 · GitHub Advisory Database · GitHub
6>D:\Epic Games\UE_5.4\Engine\Source\Programs\UnrealBuildTool\UnrealBuildTool.csproj : warning NU1903: Package ‘System.Text.Json’ 6.0.0 has a known high severity vulnerability, Microsoft Security Advisory CVE-2024-43485 | .NET Denial of Service Vulnerability · CVE-2024-43485 · GitHub Advisory Database · GitHub
6>D:\Epic Games\UE_5.4\Engine\Source\Programs\UnrealBuildTool\UnrealBuildTool.csproj : warning NU1903: Package ‘System.Text.RegularExpressions’ 4.3.0 has a known high severity vulnerability, Regular Expression Denial of Service in System.Text.RegularExpressions · CVE-2019-0820 · GitHub Advisory Database · GitHub
6>D:\Epic Games\UE_5.4\Engine\Source\Programs\UnrealBuildTool\UnrealBuildTool.csproj : error NU1605: Warning As Error: Detected package downgrade: Microsoft.Extensions.Logging.Console from 9.0.0 to 6.0.0. Reference the package directly from the project to select a different version.
6>D:\Epic Games\UE_5.4\Engine\Source\Programs\UnrealBuildTool\UnrealBuildTool.csproj : error NU1605: UnrealBuildTool → EpicGames.Core → Microsoft.Extensions.Logging.Console (>= 9.0.0)
6>D:\Epic Games\UE_5.4\Engine\Source\Programs\UnrealBuildTool\UnrealBuildTool.csproj : error NU1605: UnrealBuildTool → Microsoft.Extensions.Logging.Console (>= 6.0.0)
6>Done building project “UnrealBuildTool.csproj” – FAILED.
EDIT:
I tried deleting everything except for the Source, Plugins and Content folders and then changing my project to 5.5. That worked for me. Well, mostly…
Just to clarify on the OP, I had NuGet and Microsoft as sources in my project and I had it set to “All”. This resulted in me still having 3 errors. I then changed it from All to NuGet and rebuilt my project. THAT worked. Who knew? 