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All fairly easy but took a bit of time.
I requested a support callback and spoke to someone. They offered to collect it or I could take it to an Apple store. Chose to take it in in a Tuesday evening. Showed them the problem and they agreed it was an issue and they sent it off. Picked it up 8 days later.
It was in recovery mode when I collected it which meant a 12GB download and took ages (3 hours maybe) but if finally booted and my data was still there. Time Machine might be quicker if you do that.
I have an M2 Air. I've just had the screen replaced because the backlight was uneven. While it was away I switched back to my 2015 MacBook Pro and was shocked at how slow it was.