Article I'm going to link below has a good bit of info on what they've done. On my phone so I'm not gonna quote anything....
General gist is it's primarily consmetic, no changes to the story or adding of cut content (so the ending to 3 is the same...). Although they did make bringing the combat from the first game more in line with the combat systems from 2 and 3.
https://www.theverge.com/2021/2/2/22...s-release-date