Monterey 12.3 upgrade from 12.2 hangs when preparing for

I recently upgraded to Monterey 12.2.1 from Catalina

I'm on a MBA 2018 retina 13" and that worked fine (bar USB webcam no longer working - suspect the USB 2.0 issue many have reported)

It then popped up to upgrade to 12.3, so I did it since all files were backed up etc. the file to download is 4.38Gb which is appears to slowly.... complete and then show that's its preparing the upgrade - and there it remains indefinitely - I have 33Gb of MBA SSD disk space available

I've tried rebooting and re-running the d/l & upgrade 3 times and it hangs in the same space

any ideas