Swift is well-suited for creating user interfaces thanks to the clean syntax, static typing, and special features making code easier to write.
Result builders, combined with Swift’s closure expression syntax, can significantly enhance code readability.
Then you already have a cross platform GUI Lib called QT, that said: good luck.
Are you suggesting that GTK is an inferior, not cross-platform toolkit? I’ll have you know that GTK runs just fine on BSD (and maybe other things from Redmond), you uncultured swine!