Did you use iCloud for backups with your old iPhone? If Yes, then Is it possible that you had a lot of data related to Photos/videos on your iPhone 12 Pro 256GB AND you had Optimize iPhone Storage set to ON while using iCloud? The point that I am trying to make is that if you used iCloud and Optimized iPhone Storage on your old iPhone then you should use the same settings on your new iPhone. Double check whether Optimized iPhone Storage is set to ON on your new iPhone. If not, then set it to ON and after a few hours of optimization, the total occupied storage on your new iPhone should match to that of the old iPhone.
Of course, if you do not use iCloud for photos or backups then all of the above that I have typed will NOT apply to you.
Axel F.