On iOS (and maybe on Android devices), selecting BT microphone allows using BT speakers but might not allow using connected USB speakers.
If a user decides to change from built-in microphone to BT microphone, and the audio was routed to a USB speaker, audio will be rerouted, most probably to BT speakers.
There is currently no way to allow a web site to know which combo can work.
There is also currently no way to allow a web site to know whether audio rerouting happened.
It would be good to discuss what could be done in those circumstances.
On iOS (and maybe on Android devices), selecting BT microphone allows using BT speakers but might not allow using connected USB speakers.
If a user decides to change from built-in microphone to BT microphone, and the audio was routed to a USB speaker, audio will be rerouted, most probably to BT speakers.
There is currently no way to allow a web site to know which combo can work.
There is also currently no way to allow a web site to know whether audio rerouting happened.
It would be good to discuss what could be done in those circumstances.