Here is a short video showcasing all the games on Xbox Cloud Gaming for iOS devices.
I was surprised on how many games are available during this beta version. I think all the games available for Game Pass are there. I also loaded a game for you to be able to judge for yourself how the system works. Of course, this changes depending on connection speeds.
Remember to subscribe for more videos like this one. Also visit https://xbox.com/play if you want to try this beta edition of Xbox Cloud Gaming, included with Game Pass Ultimate.