https://www.cnet.com/news/new-apple-app-store-rules-just-made-steam-link-and-its-ilk-viable/

A new "Remote Application Mirroring" policy in Apple's App Store review guidelines may indicate there's hope for Valve's recently rejected Steam Link app. But in order to comply, the owner of the Steam gaming platform, Valve, may have to water down the app significantly compared to its Android version.

Section 4.2.7 of the rules, initially pointed out by Reuters, say that as long as everything appearing on the screen of an iPhone or iPad is simply mirroring what's happening on a local computer on the same network -- exactly what the app does -- then the app's OK, as long as it adheres to a couple of other constraints as well.