By 2021, almost no new games supported XP. However, you can find free indie games from 2005–2010 that run on XP:
Download from official developer sites or itch.io (filter by “Windows” and “free,” then test on XP). windows xp free games 2021
Interestingly, 2021 saw a unique trend where indie developers using older game engines (like RPG Maker or GameMaker 8.1) released games that were accidentally compatible with XP. Many "retro-styled" indie hits on platforms like itch.io in 2021 were programmed with such low system requirements that they could boot up on a 2003 Dell OptiPlex without issue. By 2021, almost no new games supported XP
For the true XP purist, the "free games" were the ones that came pre-installed. The most iconic of these was 3D Pinball: Space Cadet. Download from official developer sites or itch
In 2021, getting this game back became a mission for many. While it was removed from later Windows versions, the executable file (PINBALL.EXE) remained fully functional on XP systems. If you were running a fresh install of XP in 2021, you likely had to manually extract this file from the system files to relive the joy of hitting the "Refuel" target.