Don't know if you just call Microsoft Store "Xbox", but just to be clear - This is not an Xbox console in any way. This is a PC.
So you don't need to own any Xbox games.
You play Steam games on it, Epic games, Microsoft Store games, Battlenet games, Ubisoft games, Gamepass games, emulator games, your own Unity games, whatever you have around on your PC.
Ironically, you can't play a single Xbox game on this "This is an Xbox" natively, only streamed through the cloud or remotely streamed from a console.
There might be a possibility to run OG Xbox and 360 games through a third party emulator. Unfortunately I don't know how the performance is, I'll definitely check that out once I get it.