This is a play repository for learning GTK3+ on top of Wayland in Ubuntu 21.04. You may find it useful if you are in the same situation.
As a suggestion to start out, build which_display as follows
./build.sh which_display
Then, set this environmental variable
export GDK_BACKEND="wayland,x11,*"
Then run which_display. If you see this, you have indeed setup Wayland properly on your box.
./which_display Display name wayland-0 Is Wayland
Note:
The getting started guide for gtk4 is at https://docs.gtk.org/gtk4/getting_started.html
Note:
You can install gtk4 with sudo apt-get install libgtk-4-dev gtk-4-examples geany, but gtk4 only uses x11 transport as far as I can tell.