Hi, thank you for further advice. OK so I've now tried the following:
Uploaded 50 hour playthrough to the cloud. Deleted all saves from console, deleted game, deleted cache, rebuilt databases. Swapped to a different HDMI, and then reinstalled the game and updates, and started a new game (with wi-fi turned off). 1st attempt it froze on first cutscene after the character creator. 2nd attempt it froze in the character creator. 3rd attempt got through everything fine, and then it froze in gameplay in the first fight with the demons.
Bit frustrating as it was working so smoothly for so long and not sure what's causing the freezes/crashes. It feels unplayable now so think I'll end my experience here and move onto other games. Thanks for your help and patience with different tests, it was worth a shot 😊