How to add multiple AirPlay 2 destinations for streaming audio on iPhone or iPad

Apple’s update in 2018 of its streaming audio and video standard to AirPlay 2 allowed picking multiple simultaneous audio-streaming destinations while playing audio or video. In iOS and iPadOS, AirPlay 2-capable devices originally appeared in the list of available destinations with a circle (or radio button) to the right of their name, indicating they were available as part of a multiple selection.Apple changed this behavior in iOS 14.2 and iPadOS 14.2, which you may not have noticed unles