Does someone know some regular Xbox One games that will see benefits on Series X in regards to dynamic resolution (and I'm not talking about miniscule improvements like 1800p on Xbox One X -> 4k on Series X) or unstable framerate even without patches?
I can only really think of:
any other game that really struggled to reach anywhere close to 4k (with dynamic resolution) or 60 FPS?
Just Cause 4 had a 1080p to 2160p scaler on Xbox One X, and it spends a good chunk of time running closer to 1440p than 2160p, so you should see a big resolution improvement on Series X, as well as a stable 30 fps (drops below 30 fps occasionally on XB1 X).
Witcher 3 has both a dynamic resolution scaler and an unlocked framerate in performance mode, and it ran between 1080p and 1332p on Xbox One X, with framerate between 40-50 fps, so you should see a subtantial resolution and framerate improvement playing Witcher 3 in performance mode on Series X. However, since Witcher 3 is being Series X optimized next year, you're better off waiting for the optimization to play it on Series X.