I have just released gtk-fortran 4.1, based on GTK 4.4.0 and GLib 2.70.0, and generated with Fedora 35.
Concerning gtk-fortran itself, under the hood the main change is that each interface now uses the import :: statement instead of use, intrinsic :: iso_c_binding, only: (although anecdotal, the overall size gain is 6% on the 9822 interfaces).
Since gtk-fortran 4.0, new How-to were added in the tutorials section. A new gtk-fortran-extra repository was created with more examples under MIT license demonstrating applications that can be built either with or without their GUI (see that post). And a repository gtkzero_fpm demonstrates how the Fortran Package Manager fpm can build a gtk-fortran project (see that post).
gtk-fortran 4.1 was tested under Fedora 35, Ubuntu 20.10, FreeBSD 13.0 and MSYS2/Windows 10 with GFortran. And also with ifort 2021.4.0 under Ubuntu 20.10. Known issues are here.