In brief: A minor new feature is coming to the Xbox app on Windows, which will make it easier to tell how well a game will run on any given system. Microsoft hasn't revealed the fine details, but it's available now for Xbox Insiders.
Xbox Insider users browsing the Xbox app should start seeing words like "Should play great on this PC" on the store pages of some games like Doom Eternal, Forza Horizon 5, or Yakuza Zero. The Verge notes many titles as of now still say "performance check not available yet."
To enter the Insider program on Windows, install the Xbox Insider Hub app from the Windows Store. In that app, agree to join the preview program, and a selection of beta features to join should appear under "previews."
It's not clear if there will be other performance indicators beyond the one saying "should play great." Additionally, "great" performance is rather vague. It is unclear whether this means the game will run at 60 frames per second in 1080p or some other standard.
Game pages in the Windows Store and Xbox app already list system requirements. The Windows Store even uses checkmarks to indicate which hardware requirements your machine meets. Your rig's weak spots are indicated with links leading to the "about" page in system settings.
The new label seems designed to provide a general overview of expected performance. It could also help novice users who don't know much about system requirements quickly see if their computer will run the game sufficiently.