"files appear to be unsupported or damaged" after updating LrC from 9.4 to 12.1 version

Hiya,
Had a bit of a hunt on the forum for a solution, but have't come across one yet.
I recently bought a new macbook pro and transfered everything across via apple's transfer system.
This means I've gone from apple's High Sierra OS to Monterey OS, and LrC 9.4 to 12.1 version.
Now all photos in my entire LrC come up with the "the file appear to be unsupported or damaged" error.
I understand there's likely to be some changes with software as the versions upgrade, but surely there's a way to transfer that information across.
I've tried changing the location of the .lrcat file and reconnecting, but it hasn't made a difference. 
I still have my old computer and catalog working, is it possible I should try transfering it across a different way from what I did originally?
Any help would be greatly appreciated