Hi!
I have created this issue for caribou a while ago (https://gitlab.gnome.org/GNOME/caribou/-/issues/11) and it was suggested to ask here.
So my question is: is there an on-screen keyboard app/plugin that works at the GTK level of things (e.g. via GIO) and not as a GNOME shell extension? It should still work on X11 with GTK4.