https://www.techradar.com/news/apple-still-open-to-idea-of-valves-steam-link-app-to-ios

Earlier this month, Valve surprised gamers with the announcement that it was bringing the ability to stream PC games to iOS and Android devices via a dedicated a mobile Steam Link app. That app was available for Android on the Google Play Store (albeit in beta form) immediately following the announcement, so owners of Google-powered smartphones and tablets can already get up and streaming, and Valve said that the iOS version would follow soon. 

Late last week, however, Valve came out and revealed that although it had initially approved the Steam Link app, Apple had since revoked that approval,  meaning Steam Link's releaseon iOS was effectively in limbo.