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 (April 2021), new How-to were added in the
tutorials section of the wiki. A new gtk-fortran-extra repository (https://github.com/vmagnin/gtk-fortran-extra) was created with more
examples under MIT license demonstrating applications that can be built
either with or without their GUI. And a repository gtkzero_fpm (https://github.com/vmagnin/gtkzero_fpm) demonstrates how the Fortran
Package Manager fpm can build and run a gtk-fortran project.