File an issue report at bugs.funtoo.org
rj@funtoo ~ $ gimp
(gimp:14880): GLib-GObject-CRITICAL **: 10:19:51.172: g_param_spec_internal: assertion 'is_valid_property_name (name)' failed
gimp: fatal error: Segmentation fault
(gimp-org-pagecurl:14912): LibGimpBase-WARNING **: 10:19:51.227: gimp-org-pagecurl: gimp_wire_read(): error
Always try to start a program in terminal when it fails by clicking shortcut in start menu.
The error message enabled me to find the closed upstream bug report and a temporary workaround.
https://gitlab.gnome.org/GNOME/gimp/-/issues/4392