SUMMARY
I don't know how long ago, probably no more than two months, my system began crashing mostly when viewing videos in Youtube with Firefox. Although it also crashed once just having Whatsapp Web opened.
Let me point out that I didn't do any hardware change.

STEPS TO REPRODUCE
1. Open Firefox
2. Start watching videos on YouTube
3. Wait until everything crashes

OBSERVED RESULT
Both of my screens go black, but the mouse cursor remains visible and frozen.
Audio keeps working, for instance, if I'm having a remote call, the call continues, I can still talk with the other party.
If I was sharing screen, I ask the other party to tell my if my cursor moves when I move the mouse, and it doesn't.
It seems all inputs get frozen since I cannot even access any tty with CTRL+ALT+FX
The only thing I can do at this point is a hard reset.

EXPECTED RESULT
To be able to use Firefox wihout any crashes.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma:  KDE Neon 5.27
KDE Plasma Version:  5.27.9
KDE Frameworks Version: 5.111.0
Qt Version: 5.15.11
Graphics Platform: X11
Graphic Card: ASUSTeK Computer Inc. Navi 21 [Radeon RX 6800/6800 XT / 6900 XT]

ADDITIONAL INFORMATION
I usually run xanmod kernel but I tried with the general kernel and the problem is exactly the same.