Microsoft's definition of "cross-platform" generally means "Windows and mobile devices, maybe Macs"; MAUI supports Windows, macOS, iOS, Android, and Tizen, but not desktop Linux.
Generally speaking, if you want a .Net UI that works on all desktop operating systems you'll want a third-party framework like Avalonia or Uno. Yes, that's extremely annoying but .Net is generally well-designed otherwise and they have to put that signature Microsoft touch somehwere.
