I set up the player to use PiP on mobile (iOS/Android) but background audio plays back at the same time?

How to I handle background audio on mobile devices i.e. both background audio and PiP audio playing at the same time?

There is no specific default handling in the player as it may depend on the application and even on the type of content (e.g. you may continue playback of music in lower volume while navigation is spoken to you; however you may want to pause an audio book during that same interruption).

There are also some differences of what the system does and what the app is expected to do for different Android versions.

This article goes into a good deal of detail on handling this behavior specifically on Android.

And this article gives some detail on handling w/ iOS.