ObjFW  GUI framework - call for help!

So, now my 2 cents. I thought a while about it and I agree with your statements above. I'd like to add some differentiation and consider desktop and mobile target platforms.

### Going for desktop only

Taking a conservative desktop approach would mean to use Qt I think. It's just the most used cross platform toolkit that works very well and still looks acceptable everywhere. (This does not differentiate the Linux desktop any further, taking into account the GNU/Linux desktop got only 2,35% or something of the desktop market share.)

But if it comes to mobile (targeting iOS, Android, Windows Mobile, Plasma Mobile or Ubuntu Touch/UBports) you will need to use QtQuick/QML and/or Kirigami as well. That would mean to not only handle C++, but go the JavaScript/QML path as well. If we consider our users (I mean developers wanting to have a cross platform GUI toolkit) then I assume there are very few ObjC developers (f.e. coming from iOS development) who want to ditch their xib files and storyboards and start mangling QML.

### Going mobile first

If we take into account there already is a (incomplete) AppKit port by the GNUstep project I won't target the desktop as a first class citizen again, even though most of us probably like their desktops. But mobile marketshare is 59% vs 37% of the desktop with mobile still gaining space (https://www.netmarketshare.com/device-market-share).

That means most of the ObjC devs of the last years probably were iOS/UIKit developers and not developing for the desktop (AppKit), considering macOS was having 9.77% of the desktop market share in 2019 and iOS 28.23% of the mobile one (https://macdailynews.com/2019/06/03/apples-macos-and-ios-market-share-both-up-in-may-2/).

Targeting mobile first could lead to the usage of Gtk because with the efforts of the ongoing Phosh project apps are going to work mobile using the same C code basis afaik. Using Gtk themes these may even integrate into Android.

### Conclusion

To be really appealing to UIKit devs that would mean to create a Gtk wrapper which is very close to UIKit. ObjC devs thus could provide a Gtk based frontend for Android/Gnome/Phosh/Windows (Mobile) with maybe little changes, but leave it unchanged for the Apple platforms. (UIKit apps sooner or later are going to work at every Mac, despite the ongoing development of SwiftUI of course, with Swift currently not providing ObjC bindings for Linux.)

As a free surplus of taking the Gtk way you will get that the Gnome/Elementary OS/Phosh communities probably are much more welcoming an approach that allows porting Cocoa (Touch) based software than the Qt/C++ communities.

Finally I like C over C++, but that's just personal preference.