BarryK was talking in his blog about Celluloid Media Player and where the preferences for this are stored. I am not totally sure of the mechanism, but I believe this involves the "schemas" thing, with the settings framework written and stored in .xml files in /usr/share/glib-2.0/schemas
I am seeing io.github.celluloid_player.Celluloid.gschema.xml and also io.github.GnomeMpv.gschema.xml in that directory, plus the file gschemas.compiled which I think gets recompiled when any changes are made to the .xml files. Not sure if the file /root/.config/dconf/user is involved in the process or not.
EDIT:- Deleting this file restores settings to default so it would appear that this is where modifications are stored. Reading a bit more it seems that dconf is used as the gsettings backend if there is no Gconf (?).
LATER EDIT:- After close and restart of celluloid, the user set preferences come back unless I killall the dconf-service process as well as deleting the /root/.config/dconf/user data file, so maybe the process holds a backup in memory or something (?).
Notes:-
Celluloid was formerly named GnomeMPV and I think the schemas thing may be part of gnome which is why it is used. Celluloid is a front end for MPV which has its own preferences stored elsewhere as well. I have compiled celluloid-0.19 in FossaPup (some while back) and I was looking in that, rather than in EasyOS, but things should be the same I guess. Others may know more about this than me, feel free to chip in if you do.