The latest TestFlight build for Microsoft's Mixer Create app which allows live streaming of games in real time, delivers the ability to make use of one of the newer features in iOS, Screen Recording.
Screen Recording is a new feature introduced in iOS 11 that allows users to record their screen, or allow remote control or streaming via third-party apps. TeamViewer, for example, supports remote control of an iOS device via Screen Recording, and now Mixer is joining in on the action, with users now being able to stream their apps and games to the Mixer live streaming platform via the Mixer Create app.
To stream an app or game via Mixer Create, simply open up the Control Centre and tap Screen Recording (you may need to enable it via Settings), then tap Mixer Create.
It's likely this feature will be making its way to the public version of the app soon, but for now you'll need to be in the TestFlight program and have the latest build installed.