The Steam Link app announced earlier this month is already in beta on Android, but iOS users may not get to experience it.
According to Valve, the app has been rejected from the App Store and a follow-up appeal was denied.
Similar to the Steam Link device for TVs, the free Steam Link app would allow users to play games from their Steam libraries on their devices if that device was connected to a host PC via a wired or wi-fi network. The app supports Steam controllers and several others. It released in beta on Android earlier this week, but the full version for iOS, planned for a May 21 launch, was nowhere to be found.
According to Valve, Apple approved the app on May 7, after which Valve announced Steam Link for iOS and Android to the public. The next morning, Apple revoked the approval due to "business conflicts that had allegedly not been realized by the initial review team."
A subsequent appeal from Valve did not change Apple's decision, which unfortunately leaves the app as an Android-only release unless Apple reconsiders.
It is unknown whether or not the planned Steam Video app (which lets users stream Steam movies and TV to their device) will be similarly affected. Steam Video is planned for release later this summer.
Apple is known for keeping tight control on its ecosystem, and has previously prevented companies from releasing apps that are essentially storefronts for other services. It's likely this is at least part of the reason behind this rejection.