Update on copy/paste being broken on GIMP/Inkscape on macOS (and as it turns out, TIFF loading is also broken on Windows): They won't fix it, because their image loader is legacy on macOS and Windows, but also there are no plans to bring the non-legacy image loader to those platforms.
https://gitlab.gnome.org/GNOME/gimp/-/work_items/6569#note_2853567
I guess GTK is now deprecated and unmaintained on anything that isn't Linux, and with it every app that uses GTK.