Still all with max frame rates (besides Dark Souls 1 probably) and way faster loading times. And 16x af.Bonus review from The Register: https://www.theregister.com/2020/11/05/xbox_series_s_review/
Any 360 games that got One X enhancements will run at 1440p. I believe the remaining 360 titles will run at 720p on all Xboxes.