Oooh interesting.
Further to my earlier posts, KB5034441 installed quietly on it's own on one of the four win 10 machines it failed on earlier - this was without any re-attempt to install it manually (I saw no point as this approach had failed on 2 other machines) or doing anything to bitlocker or recovery partitions as per some of the solutions knocking about (all of which seem highly technical & way beyond the capabilities of most lay people).
Hopeful that it had been fixed 'back end', I just tried on the other 3 it failed on. No go.... same error code 0x80070643 on those (all of which are all HP 10th gen machines, though I doubt that has anything to do with it, as the XPS is also a 10th gen & also has bitlocker enabled).
I'll leave it to do like the Dell XPS & Just Work at some point, or wait until it is pulled & replaced by MS. Which they jolly better. The solutions offered don't seem to work for everyone.