Been meaning to start this game up again. Haven't played it since probably the Sept/Oct 2016. Can I assume any progress I made before is null and void? I'm getting the impression that everything is different, including the worlds.
In your case, yes, but even if you could continue I would recommend starting again. These changes are HUGE and many of them are at the beginning of the game so loading an old save would skip some of the new stuff and experiences. I swore I wouldn't start again but I feel I have to now, and I'm fine with that.
The PS5 Exists.