RootCauseunvalidated
The 9.0.0 version of that package dropped the .NET 6 target framework — when you upgraded to the 9.0.0 version of the package. Tension: you started getting the .NET Standard implementation. Outcome: The recommended solution would be to move your project to .NET 8.0 or .NET 9.0, or alternatively stay on the 8.0.0 version of the package.
91abcbf6-ea33-4b03-9c2a-3c9f6b391871
The 9.0.0 version of that package dropped the .NET 6 target framework — when you upgraded to the 9.0.0 version of the package. Tension: you started getting the .NET Standard implementation. Outcome: The recommended solution would be to move your project to .NET 8.0 or .NET 9.0, or alternatively stay on the 8.0.0 version of the package.