I did some research and made a plugin for audio manipulation on iOS. If you manually call FAppEntry :: Suspend (bool bIsInterrupt) on the iOS build, the sound will be muted, as if the application was minimized. The sound does not turn back on in any way. I’ve tried calling manually
FAppEntry :: RestartAudio ()
FAppEntry :: ResumeAudioContext ()
GEngine-> GetMainAudioDevice () → ResumeContext ();
AudioMixer only logs that it has done its job
FAppEntry :: Suspend does something that kills audio on iOS 15.
It is called in the iOS App Delegate from any system activity that deactivates the game.
Third party audio engines should work fine.