They dropped the "Core" suffix with v5 in 2020, since at that point there was no longer naming confusion.
While Microsoft doesn't have their own framework supporting Linux GUI apps on the modern .NET runtime (MAUI does Mac/iOS/Android but not Linux), there are third-party ones like Avalonia.
Dropping the "Core" suffix introduced more naming confusion. Before that, ".NET" was often used as a shorthand for the (now legacy) .NET Framework. Which makes googling for Core-specific things much harder than it needs to be.
While Microsoft doesn't have their own framework supporting Linux GUI apps on the modern .NET runtime (MAUI does Mac/iOS/Android but not Linux), there are third-party ones like Avalonia.