Microsoft gave some explanations on how the Series S backwards compatibility mode works with older games. Especially those that have already been optimized for One X. These improvements will not be compatible with the Series S.
The future low-cost Xbox, the Series S, will not support improvements that may have been made on One or Xbox 360 titles to make them run better on the current Xbox One X.
All older games that will run on the Microsoft platform will run as they did on the current Xbox One X.... One S. They will then be optimized by the console in "the best possible conditions and respecting the original ideas of the developers"
The change in the architecture of the AMD APU would have nothing to do with it. However, the Series S has less RAM than the One X. And this would be one of the main causes of this "incompatibility".
Whether it's increasing the number of frames per second displayed on the screen, supporting HDR, or increasing definition, developers had worked hard to make One X make their titles look better. Sometimes it took them months to fine-tune and refine everything down to the last detail.
The S-Series will handle the enhancements on its own
There's no need to go back to work: the Xbox Series S will take care of it! Even if we ask to see. From our point of view, it's quite possible that the developers still have one operation to perform: that of implementing a sort of "Series S" profile in their game.
Microsoft says that players "can expect better textures, higher and more stable frame rates and frame rates, faster loading times, and Auto HDR.