7 days in now with the M1 Mac mini and Ultrafine 5K ... I am delighted with my purchase.
The only issue I've incurred 'occasional jagged widget line' (or 1" column of misaligned pixels as others have described) is resolved very easily by enabling hot corners in Mac OS. Set a corner to 'Lock Screen', use it and the issue goes away ie. no need to reboot Mac. Other than that, it's performing superbly for me. My alternative choice was ponying up for the Pro XDR, but a quick glance in their owners thread suggests it has niggles of its own.
I checked in the System Report (Apple Logo -> About This Mac -> System Report -> Thunderbolt) and it seems to indicate my display has a firmware release of v43.1 (at least I'm assuming that's the display f/ware)