GTK on macOS is completely fine, unless newer versions of GTK have borked it. We use GTK2 for Ardour (cross platform DAW) and there are almost no issues. I did contribute numerous important patches for the quartz backend along the way.
Gtk3 has a Quartz backend and Pidgin 3 will be native on Mac OS. It builds and runs now, but packaging has been a pain so I haven't worked that into our CI yet.
GTK3 is slightly better than GTK2 on macOS and GTK4 is getting a lot better with a paid developer working on it.
Pidgin will be in Gtk4 one day.. But right now we're still trying to replace deprecated API that we're using with Gtk3...