I take it back, mine was just fixed with a reboot (must've forgotten to reboot after my driver updates). Either way I'll push a safety rebuild for ya. Make sure you have a fully updated system and have rebooted.

It doesn't appear to crash anymore ?

Nevermind, it just crashed again..

You'll need to install gnome-mpv-dbginfo, run gdb gnome-mpv 2&>1 | tee ~/gnome-mpv.txt, type r and press Enter to run, let it segfault, then run backtrace full, Enter, then quit + Enter. Upload the text file here.

All that function is calling is g_application_run, there isn't anything special going on. There's also no upstream glib issues and I'm not seeing anything on the celluloid tracker about it either. This issue is fairly common with glib and GTK applications though, can see similar reports for other applications ranging from gimp to deadbeef. That aspect of the gio codebase hasn't been touched in 12 years either.

So I'm wagering it isn't related to our glib upgrade, especially since it isn't happening on my system (my issue was separate), there was no changes to that code, and there was only specific ABI additions. Do you have a second system where this is being affected? Have you tried rolling back the upgrade and testing then? Or selecting an older kernel on boot?

Someone mentioned in #solus-dev that it could have something to do with KDE Connect, and I can confirm that: If I wake up my phone that is connected through kde-connect, gnome-mpv crashes and If I kill kdeconnectd, gnome-mvp stops crashing.

Edit: I think this is the relevant log entries in journalctl:

aug 22 20:25:57 kim-solus kdeconnectd[5607]: Connecting to deprecated signal QDBusConnectionInterface::serviceOwnerChanged(QString,QString,QString)
aug 22 20:25:57 kim-solus kdeconnectd[5607]: kdeconnect.plugin.battery: No Primary Battery detected on this system. This may be a bug.
aug 22 20:25:57 kim-solus kdeconnectd[5607]: kdeconnect.plugin.battery: Total quantity of batteries found:  1
aug 22 20:25:58 kim-solus io.github.GnomeMpv[5336]: **
aug 22 20:25:58 kim-solus io.github.GnomeMpv[5336]: GLib-GIO:ERROR:../gio/gdbusconnection.c:4220:invoke_get_property_in_idle_cb: assertion failed: (error != NULL)
aug 22 20:25:58 kim-solus audit[5336]: ANOM_ABEND auid=4294967295 uid=1000 gid=1000 ses=4294967295 subj=unconfined pid=5336 comm="gnome-mpv" exe="/usr/bin/gnome-mpv" sig=6 res=1
aug 22 20:25:58 kim-solus io.github.GnomeMpv[5336]: Bail out! GLib-GIO:ERROR:../gio/gdbusconnection.c:4220:invoke_get_property_in_idle_cb: assertion failed: (error != NULL)
aug 22 20:25:58 kim-solus gnome-shell[1769]: Received faulty track artist metadata from org.mpris.MediaPlayer2.kdeconnect.mpris_0234ba3b67254ded848fd5b7e36b752c; expected an array of strings, got Munro Live (string)

I forgot to mention that I did a rollback to before the sync and everything worked then, but started crashing when I updated again.

I'll file an issue on their bugtracker. Downgrading kdeconnect to 21.04.3-42 seems to work as a workaround for now.