Oof, as much as I'd like to, migration to Swift/SwiftUI is just not practical at this time. Our application is very big with a lot of distinct parts (think Xcode but with more parts) so this is not trivial to do even if it's one file at a time. I've got a team working on porting the Windows MFC version of our application to .NET and they've been working on it for 3 years and still aren't done! Our application is available for Windows, Mac, and Linux and one of the nice things about ObjC is that it can be mixed in with C/C++ code which makes writing multiplatform code very easy. I did look at perhaps writing all new GUI code in Swift a few years ago when it first came out but had problems with the ObjC and Swift bridging and gave up as I had more pressing things to work on.
Topic:
UI Frameworks
SubTopic:
AppKit