It seems that the [Timeout] attribute support has been removed from NUnit 4.5. All tests fail with the error "TargetFramework doesn't support timeout on tests".

This was still working in NUnit 4.4.

The only change I've done was in my test projects where <PackageReference Include="NUnit" Version="4.4.0" /> has been updated to <PackageReference Include="NUnit" Version="4.5.0" />

Used framework: net9.0

Note:
When switching back from NUnit 4.5 back to NUnit 4.4 all tests run and complete successfully.