LibraryFrameworks value below had targeted netstandard2.1 inline with the rest of the libraries. In order to facilitate phasing out of support of this library, we've done a couple things:ExecutableFrameworks and LibraryFrameworks, we've defined a new boolean property TargetNetStandard and removed the netstandard2.1 target from LibraryFrameworks. In order to remain backwards compatibility, TargetNetStandard defaults to true.TargetFrameworks definition was added which adds the netstandard2.1 target alongside the standard library frameworks.<TargetNetStandard>false</TargetNetStandard>, the default set of target frameworks should include netstandard2.1;net6.0;net7.0;net8.0 (when it's a library type and not an executable type). If the user specifies false, then the netstandard2.1 target should be excluded.TargetNetStandardFalse appears to update its targets correctly to indicate that it is no longer targeting netstandard2.1. However, running dotnet build with either debug or release targets results in the duplicate attribute exception, which prevents tests from running. Deleting obj/bin folders has no effect on this behavior, except that it will change which test project receives the error. I imagine this is just dependent on the order the projects are discovered and built rather than some sort of phantom shifting error.