Do I understand you correctly in that this could be OS or hardware (or any number of other things)? Just trying to fully grasp.
You posted the messages on the screen originally, those are kernel ring buffer messages that have been configured to show into the console. You can tweak what shows into the console (in terms of priority) via kernel parameter, when you
sysctl -a | grep printk you will see the defaults and you can change them by editing
/etc/sysctl.conf [1] . You can also change the level at runtime with
dmesg -n $level [2] or just remain logged in and keep them having printed realtime e.g. with
dmesg -ew.
Anyhow, you saw some messages printed in the console before your machine froze, but they are also logged via
systemd-journald and should be retained in the logs. But there were none (from the screen) there (as you had shared
journalctl -k -b all). Given the fact that during an emergency reboot, disabling VMX is something routine, I think it was complaining about issues during that (see also my earlier post and comments within the code). And because it was also in that stage of rebooting, it was not possible to flush those messages onto the logs on the disk. Instead, the machine froze as per your report. So that alone does not really help analyzing the issue at all because all one knows is there was an emergency reboot attempt (likely) that failed in and of itself.
There was nothing in the logs that could point out why the emergency reboot had been even triggered, the logs just abruptly ended, so one can be assuming writing onto the disk was not possible anymore after certain point. So the only thing to focus on were the MCEs. Those are Machine Check Exceptions (sorry, I could not find some satisfactory source on explaining them nicely and consistently, but the usual forums will give you an idea) and basically it could be anything hardware related, or simply kernel having trouble interacting with it. We did not quite manage to find out exactly what they pertained to. Also, could be red herring (in relation to your freezes).
[1]
https://www.kernel.org/doc/html/next/core-api/printk-basics.html
[2]
https://manpages.debian.org/bookworm/util-linux/dmesg.1.en.html
