@louis I am definitely going to switch from Ubuntu to another distro pretty soon, and I have been torn between standard Debian with Xfce, or Mint with Cinnamon. I think I will go with Xfce because they are mostly keeping up with the latest Gtk. They long ago moved to Gtk+ v3 and are gradually transitioning to Gtk4, probably to prepare for the larger transition to Wayland.
But Cinnamon has forked Gtk+ v2 into its own widget toolkit now, so it is kind of its own platform based on GLib and GObject, and it seems to be quite stable and over all a good user experience. It would be nice to have some of my apps programmed to work with either Cinnamon or Xfce. We will see if they will be able to port it to Wayland without the help of upstream Gtk.