We've already seen some fantastic Starfield mods on Xbox since the June update arrived last week, and some of the latest examples allow the Xbox Series S version to reach a high of 120 frames per-second!
This is documented in the video you see above, which shows how certain Starfield mods lower the visual quality in order to provide a smoother experience on Xbox Series S. As shown at the 1:24 mark, the mods that are used here include "Uncap FPS for Series S", "Performance Tweaks (Series S)", "Performance Shadows (Series S)", "Remove Grass", "Crowd Reducer" and "No God Rays".
Now, as cool as this is, there are some obvious drawbacks as well. 120FPS is the absolute max the Xbox Series S can reach, but it often doesn't go that high - so an uneven frame rate is to be expected. The visual quality also takes a big hit as you'd expect, with the "Uncap FPS" creator even stating that screen tearing can be an issue when using it.
Feel free to experiment with these mods if you wish (they're free after all), but keep in mind they're not created by Bethesda, so you shouldn't expect a perfect experience by any means. It's also worth noting that Starfield was never meant to run at 120FPS on Xbox Series S, so any modifications like these should be applied at your own risk.
Nevertheless, it's fascinating to see a game like Starfield reaching 120FPS on Xbox's little console!