UnrealBuildTool.UnrealBuildTool.GetAllServerPlatforms() doesn’t exist anymore.
If you have a dedicated server target (MyGameServer.Target.cs), I believe the correct way to define the platforms now is to annotate the class and delete the GetSupportedPlatforms method
[SupportedPlatforms(UnrealPlatformClass.Server)]
public class MyGameServerTarget : TargetRules
{
...
}
Haven’t tried it yet but I’m seeing the same changes on Epic’s commits at https://github.com/EpicGames/UnrealEngine/commit/6748a24fb192420b4ead6779e54a12b0001bfa8f