In 2013, Microsoft announced that it would be possible to turn any Xbox One into a dev kit, or almost. And they did!
The process requires you to create a developer account and paying $20 but after that you can code your own UWP apps or download buddies' apps and install them on your Xbox One. In other things.
Microsoft has kept this possibility for the Xbox Series, So the UWP version of RetroArch works on the Series X right now. The process is the same as on Xbox One and we imagine that it is the same for the Series S.
Casually Microsoft is the only one of the three manufacturers to offer this feature.