The Xbox team gave us the sad news back in November that the FPS Boost program for Xbox Series X and Series S was finished adding new titles for now, and they've recently reiterated that they don't know if it'll ever return.
In an interview with TechRadar, Xbox Director of Project Management Jason Ronald once again pointed out that FPS Boost (and backwards compatibility in general) comes with some major technical hurdles, and due to the team being unable to change a game's code at all with FPS Boost, it makes certain titles impossible to support:
“One of the challenges that we have on some of the enhancements and the capabilities is that we do all of this with no code changes to the actual original game. So, as we identify new techniques of enhancing and optimizing titles, oftentimes, we know it won't work on all games."
"A lot of times, we try to come up with solutions, and we see if we can work through those issues. But since we treat it as a black box, we don't have the ability to change the game code directly."
As previously mentioned, Ronald stated that "to be honest, we don't really know right now [whether FPS Boost will return]" in response to a question from the team at TechRadar, which echoes his comments from back in November.
At the time of the original announcement, Ronald told the Iron Lords Podcast that "we're going to continue to look for new opportunities and new ways that we can enhance titles, but we don't have anything in the immediate future," explaining that "we're kind of finding where some of the limitations of our current technique is."
If you're interested, we've got a complete guide to all 100+ FPS Boost games here at Pure Xbox.