Backward compatibility is one of the key factors that gamers look towards when buying a new console. It gives you access to a wide library of games from older generations, and this time around both Sony and Microsoft are offering it on their devices. However, the Series X has an edge when it comes to backward compatibility.
Most backports of older games on the PS5 are limited to 60 FPS, but its Xbox counterpart is able to achieve a full 120 FPS, significantly enhancing the experience. If you’re wondering that this might be cos the latter has slightly more powerful hardware, then you’re wrong.

According to Rocket League developer, Psyonix, enabling 120 FPS on the PS5 “requires a full native port”, while it can be enabled on the Xbox Series X and S with a simple patch. Keep in mind that we’re talking about older titles accessible on the next-gen consoles via the backward compatibility feature.
This means that the game engine needs to be updated to include frame rates up to 120 FPS which can be quite hard to do on a console where you’re often running a dynamic resolution mode, with upscaling features like checkerboard rendering. Enabling 120 FPS on an engine that doesn’t natively support it, therefore requires rewriting the code for all the above-mentioned parameters.
Some engines simply don’t support 120 FPS, and this is similar to when older console games are ported to PC, and the final product is a title that simply can’t be made to run at 120 FPS without glitches and speeding up the animations as well.

Most studios (especially indies) can’t afford to divert that much manpower to bring 120 FPS support to older titles when they already have projects in the pipeline. As per DF chief, Richard Leadbetter, the reason behind this is that the previous-gen Xbox consoles already supported 120 FPS, but it was almost never used.
Microsoft was hoping to leverage newer DX12 technologies such as Variable Rate Shading and Sampler Feedback to make up for the lack of raw processing power and enable 120 FPS in less intensive titles. Although it didn’t quite work at the time, it has made porting games to the new consoles much easier with 120 FPS support nearly out of the box.