Xbox one stops responding after update on 1 December 2020

I'm based in the UK. My Xbox One S updated itself on 1 December 2020, to the version listed on the en-US version of the xbox website (OS version 10.0.19041.5481), which is different to the OS version listed on the en-GB xbox website (10.0.19041.5082).
Playing Call of Duty Modern Warfare on 2 December 2020, a couple of hours in to the session the game froze. I rebooted the console, CoD started loading, but wouldn't complete. Tried a hard reset. Again could start CoD loading, but it wouldn't finish. A
few more resets later I tried Forza Horizon 4, and it wouldn't finish loading either, it showed the splash screen, started playing the music, and then the sound stated skipping like a stuck CD. Very annoying, and wouldn't load further, even when left for 20
minutes or so. I've now completed a factory reset, and an offline reset. Reinstalled Forza Horizon 4. Had a different loading glitch, restarted the system, and tried again, and it loaded! Then paused on one of the first option screens, then progressed
to the game. 30 seconds in, the game stuck for about 5 seconds, then carried on for another 10 seconds or so, and then stuck with 80% of the screen having changed, put part of it not changing. I could scroll through the different car views, but that was about
it.

Sometimes the controller becomes unresponsive (and I've tried two different controllers) even when accessing the settings app, and then won't recognise any commands from the controller. Sometimes it will later catch up, with a button press 30 seconds later,
but mostly not.

Now been on hold to Customer Services for 40 minutes, even though it was a scheduled call. And this is the second time round...

Any ideas for what may be wrong, and what I should do next?

Thank you

:)