I think you may want to use for device in /dev/disk/by-uuid/*

That doesn’t explain why you aren’t seeing messages. I see there is a shebang at the start of the script. Can you confirm that the script has the executable bit set for the root user?

It works with USB interfaces using passthrough. But yeah doesn’t make a lot of sense.

From Archwiki > xrandr:

Tip: Both GDM and SDDM have startup scripts that are executed when X is initiated. For GDM, these are in /etc/gdm/, while for SDDM this is done at /usr/share/sddm/scripts/Xsetup. This method requires root access and mucking around in system configuration files, but will take effect earlier in the startup process than using xprofile.

Mount the drive with the user or group as plex. See mount options uid and gid. You can also set precise permissions on the mount point (using options at mount time) to let plex access a subdirectory.

Yet

You could try organic maps.

Try this:

for file in ./*
do
    echo "$file"
done

To do some substitution operation om the filename you can use Bash Parameter Expansion.