@ all
So, I restarted the system and, as usual, the X server did not start:
- Black screen
- System fan spinning fast
- Command prompt still available through Ctrl+Alt+F2
at this point I was going to format the usb stick once again. But I thought: why not to try it on my desktop first (Nvidia RTX 3080)?
Well, incredibly it booted up, perfectly, in 4K!
I decided to immediately try it again on my laptop, for sorting out somehow what the culprit of the issue could be. And, incredibly, it booted ok again on my laptop. But why?
So, I rebooted again on my laptop, and this time the X server started, but only in 800x600 pixel.
Restarting once again, it booted up normally.
So, at the end of the day, I think that I can safely say that at least for the video chip of my laptop (Intel Iris Xe - driver Intel i915 -) the detection of the screens is buggy. This should have nothing to do with the kernel.
I have also tried to boot and reboot on the desktop PC. The first time it booted, the second time I got black screen (and now I'm back on the laptop, on which it booted fine). So it looks like the X server always works when the driver is switched (from Intel to Nvidia or vice versa), and never works more than twice when the system is rebooted on the same machine. Therefore, another explanation may be that there's something wrong within the shutdown procedure.