No panic as I've solved the problem but thought it might be worth reporting. Just upgraded my system to 24.1 and it froze during reboot. Connected a monitor and nothing, wouldn't boot at all. After an hour of trouble shooting I finally, in desperation, switched the Bios to boot in Legacy mode rather than UEFI and, wonder of wonders, with sighs of relief, it came up!
Does the 24.1 upgrade disable UEFI booting in some way? I'm now running Legacy - which is fine, but it was all very odd that I had to change it.
Did you upgrade in-place? If yes, that would be strange indeed. Otherwise, maybe used the MBR option during a fresh install?
Yes, I upgraded through the GUI. It downloaded all the upgrade files including the new kernel, then rebooted. That's the last I saw of it! :-) It took me a long time to find the problem. Switching Bios boot options is not the first thing I thought of.
PS - I have since done a new install over the top of the old (importing the old configuration) just to make sure all was squeaky clean. I've left the Bios in Legacy mode.
now, that is surprising. Sorry, no idea.