I experienced similar symptoms twice yesterday. Everything froce up with a glitched screen, but I was able to turn the screen on- and off, to switch between a black- and the glitched screen state. A (very) long press of the power button triggered a force-reboot, but nothing else worked. (Note that there’s no sd card in my FP4 at the moment.)
I posted a picture/video of the behaviour in the random reboot thread, since I thought it might be related. Haven’t experienced the behaviour since.
Do you have 5G enabled? That’s been identified as a likely common culprit in the reboot thread I mentioned above.