I think for right now, you'd have to use the C interop and link against something like GTK or other GUI library. I don't think SwiftUI specifically would ever work well cross-platform, it has so many Apple-isms.
There's also Swift/Win32, but it's MVC. You could also use the interop and use QT as well.
I don't think any of those are necessarily good solutions, but they are there.
What sort of things are you referring to when you say "Apple-isms"? Not that I doubt your claim -- I just don't do much UI development so I don't have a good reference for what things might be 'platform specific' in that way.
Yes there’s nothing all in one yet. But these are promising directions. Tokamak isn’t abandoned, members are involved in core Swift changes that it depends on and have made progress recently with embedded Swift.
I think for right now, you'd have to use the C interop and link against something like GTK or other GUI library. I don't think SwiftUI specifically would ever work well cross-platform, it has so many Apple-isms.
There's also Swift/Win32, but it's MVC. You could also use the interop and use QT as well.
I don't think any of those are necessarily good solutions, but they are there.