For anyone who finds this answer later, the exact solution is:
- Open Visual Studio (you can select Continue Without Code)
- Navigate to Tools > Options > NuGet Package Manager > Package Sources
- You’ll most likely see only one source titled “Microsoft Visual Studio Offline Packages”
- Click the “+” button to add a new source
- Name it whatever, and type “https://api.nuget.org/v3/index.json ” for the source
- Click the “Update” button and then make sure it’s checked
- Run GenerateProjectFiles.bat again it should work now!