Debian package numbers by GUI toolkit:

GTK+ 2: 94
GTK+ 3: 822
GTK4: 166
Qt5: 769
Qt6: 980

#GTK4 was released on 2020-12-16.
#Qt6 was released on 2020-12-08

Those numbers proved that GTK4 is so bad that 3rd-party developers just don't want to use it.
Many great GTK+ 2/3 apps migrated to the Qt ecosystem, because GTK4 is just a no-go.