What's in the etc/profile of your profile?

It should have something like

--8<---------------cut here---------------start------------->8---
export GIO_EXTRA_MODULES=\
"${GUIX_PROFILE:-/gnu/store/2amj32ic81b9inf32a88y8gg5y7019wx-profile}/lib/gio/modules${GIO_EXTRA_MODULES:+:}$GIO_EXTRA_MODULES"
--8<---------------cut here---------------end--------------->8---

since the glib package definition has this:

--8<---------------cut here---------------start------------->8---
   (native-search-paths
    ;; This variable is not really "owned" by GLib, but several related
    ;; packages refer to it: gobject-introspection's tools use it as a search
    ;; path for .gir files, and it's also a search path for schemas produced
    ;; by 'glib-compile-schemas'.
    (list (search-path-specification
           (variable "XDG_DATA_DIRS")
           (files '("share")))
          ;; To load extra gio modules from glib-networking, etc.
          (search-path-specification
           (variable "GIO_EXTRA_MODULES")
           (files '("lib/gio/modules")))))
   (search-paths native-search-paths)
--8<---------------cut here---------------end--------------->8---

Maybe try to install gsettings-desktop-schemas, see if that helps.

-- 
Pierre Neidhardt
https://ambrevar.xyz/