I mostly do backend systems, with web based UI tooling, which is quite a bit different. I do have a fair amount of experience with C# as well as migrating codebases from older .Net to .Net Core/5+ under Linux. Been looking into this thread for a few years now.
Have you looked at, or considered the Avalonia[1] UI toolkit. It's what MS used for their git-credential-manager (formerly *-core)... I'm not familiar enough with the codebase to know how easy it would be to convert/port to another UI framework for LaunchBox or BigBox's UI though. Part of me thinks that an SDL[2] library for C# may be better for at least BigBox's interface, but not sure what's in place for this. There's mention of MAUI above (for Android), which has seen some movement on a Linux branch, not sure on performance though.
https://avaloniaui.net/
https://www.nuget.org/packages/sdl2.nuget
