Manage Nuget Packages shows this white panel where searching doesn’t work, there is no version selection, etc.
Is it possible to replace or add in the context menu for References original nuget manager that sometimes shows in the Project menu?
Also note that mscorlib.dll does not exist for .NET Core, it’s only available/needed for classic .NET 4.8 and below (not .NET Core) projects. In what scenario do you see that error dialog?
Turns out this IDE feature is not supported for Core, and should never have been enabled (VC# doesn’t have it, only for Classic). We’ll “fix” this by also disabling it for Core projects.
Sorry if this (probably) was not the resolution you were looking for, but this is on Microsoft’s side, not something we can influence.