glib 2.74.0 and newer breaks XFCE and most GUI applications (unable to start)
After days of troubleshooting I've figured out that, on this specific system,upgrading glib2 to 2.74.0 or any newer version (from the newest working version, 2.72.3-3) results in XFCE being unable to start from either lightdm or SDDM or even just plain startx. I am still able to start KDE from SDDM with no issues--only XFCE is affected.
It crashes instantly and silently. I can't spot any meaningful error message in either journalctl -u sddm.service or /var/log/Xorg.0.log, though I'm happy to share both logs.
I'm on Arch Linux, LTS kernel, and this issue seems to be consistent on every recent version of the LTS kernel. My unique hardware combination (which I imagine must have something to do with this, since I can't find any mention of this issue online) is: AMD Ryzen R7 2700X CPU, R9 Fury 4GB GPU, and an X470 chipset motherboard.
Possibly related behavior is, whenever I upgrade glib2 to a problematic version, it's not just that I cannot start XFCE on the following boot. Also, immediately on the current session as soon as the package is upgraded, most GUI applications including all GTK-based applications fail silently to open, other than a SIGTRAP.
I've gone on #xfce-dev to report this and ask which component of XFCE I should report this to. They suggested this might not be specifically an XFCE bug, thanks to the previous paragraph. I've also submitted this bug to the Arch Linux tracker in case it's an issue downstream: https://bugs.archlinux.org/task/76413