Smartwatches are not on the list, but modern devices gain access to various applications, so one player decided to test an interesting idea. He launched Xbox Game Pass (Cloud Gaming) in a browser.
A proper controller is required. Playing on a watch is not entirely convenient, but feasible. This proves the potential of Microsoft’s offering: a player only needs an internet-connected device and a browser.
At the link, you can find a video featuring a short clip of playing Slay the Spire.