So I tried creating my first GTK 4 program using example-0.c using https://docs.gtk.org/gtk4/getting_started.html#basics guide, but I got the later-described error regarding G_APPLICATION_DEFAULT_FLAGS.
So I'm assuming my GLib version is older than 2.74. I used the command:
pkg-config --modversion glib-2.0
and got
2.72.4
The problem is that when I tried upgrading the package, nothing changed. I remember trying to upgrade libglib before (I forgot the commands I used), but it said that it already has the newest version, which is false because, according to https://docs.gtk.org/glib/, the newest version is 2.76.
Why does it think that the current version is the latest one; how to fix that and upgrade GLib?