I have an HP All-in-One 27-a275na.

All was working well under Win11 23H2 and just downloaded the ISO for Win11 24H2. Kept only my data to get the benefit of having the best possible install and then reinstalled only the latest versions of the apps I wanted.
Have checked for corrupted files (none found), deleted the Facial Recognition (Windows Hello) Software Device in Device Manager & Rebooted.
On restart the machine fails to start camera and asks for PIN and then when I try to setup Windows Hello Facial Recognition I get the Error Message " Sorry, something went wrong. Couldn't turn on Camera. Make sure it's working properly.
On checking the camera app it all appears to be working properly, and the windows settings allow apps to contact it!