GNOME Shell user shell and composite manager MUTTER completely transposed to use the GTK4 library and got rid of the rigid dependence on GTK3. In addition, the dependence of Gnome-Desktop-3.0 is replaced by Gnome-Desktop-4 and Gnome-BG-4, and Libnma on Libnma4.
In general, GNOME is still attached to GTK3, since not all applications and libraries are spoiled on GTK4. For example, on the GTK3 remain webkit , Libpeas , Libibus, Viewer of the documents Evince , video player total , viewer of images EOG, Boxes, ConNECTIONS , disks, Simple-scan , Photos and System Monitor.
/Media reports cited above.