The promise of Xbox Cloud Gaming, included with an Xbox Game Pass Ultimate subscription, has always been strong. Subscribers gain access to the full library of Xbox Game Pass on all devices that support Xbox Cloud Gaming, including iOS and Windows-based phones, tablets, and laptops, PC, as well as Xbox consoles. The opportunity to do bigger things has always been there, however, and Xbox Cloud Gaming is now taking that step. Fortnite is now free to play via Xbox Cloud Gaming, no subscription required.
Microsoft has published a support article and Reddit post that explains how to play Xbox Cloud Games on the Steam Deck. The process currently involves installing the Linux version of the Microsoft Edge browser in the desktop Linux environment.