Looks like SysRq keys are not enable in your distro by default, don't know the reason but Fedora kernel devs would known better than me.
Just for curious, did you installed some gnome extension recently? try this
grep -i gnome-shell /var/log/syslog* | grep -i exten
What about dmesg? if it's a hardware problem (and it looks like, but I may wrong) dmesg will print some usefull data
sudo dmesg -Tw
-T form human redeable timestamp and -w to follow (like tail -f)
Also, about that hard reset that you did, Linux magic keys are your friends if your are not facing a kernel panic, I have this key combo engraved in my head like a rune:
Press and hold Alt + PrtSc (not Alt+Gr) and then press only one time each (and while holding Alt + PrtSc) E + I + S + U + B
PrtSc maybe be SysRq in your keyboard depends on the manufacturer, architecture or how old it is. Also wait one or two seconds between keys when pressing EISUB.
Edit: the rune in my head was wrong, fixed it
Probably is not going to make your phone experience much better but I followed this to disabled (not uninstalling) some stock apps on stock Android phones, works great and if you made a mistake it's easy to rollback.
No se podría haber explicado mejor.