The AudioMixer is the Unreal Audio Engine native audio rendering layer. It was in beta until 4.24 where it became the default audio rendering pathway for Unreal Engine. We only did this after successfully switching Fortnite to using it on all of Fortnite’s supported platforms including Android, iOS, and Switch.
Fortnite is our yardstick for Unreal Audio Engine’s mobile platform support, so iPhone 6S/6S Plus or newer.
Are you on an older iOS device?