Error: Package Microsoft.AspNetCore.Identity.EntityFrameworkCore 5.0.8 is not compatible with netstandard2.0

After installing a package, OmniSharp hit me with this:

    [fail]: OmniSharp.MSBuild.ProjectLoader        Package Microsoft.AspNetCore.Identity.EntityFrameworkCore 5.0.8 is not compatible with netstandard2.0 (.NETStandard,Version=v2.0). Package Microsoft.AspNetCore.Identity.EntityFrameworkCore 5.0.8 supports:  - net5.0 (.NETCoreApp,Version=v5.0)  - netstandard2.1 (.NETStandard,Version=v2.1)

followed by a lot of warnings like :

[warn]: OmniSharp.MSBuild.ProjectManager        Expected project reference '..' to be already loaded for project API

and all of a sudden I have 58 errors in my project:

The type or namespace name 'Entities' could not be found (are you missing a using directive or an assembly reference?) [API]

I tried removing the package, I added "omnisharp.path": "latest" in settings.json, and I tried deleting Nuget's cache: dotnet nuget locals all --clear .None of these helped. What do I need to do?