[1727706962]

That's exactly what I do - An aggregate device (called 'Forced Onboard Mic') with only 'MacBook Pro Microphone' selected.

This is configured from 'Audio MIDI Setup.app'

Apps configured to use that as their input device then don't reconfigure themselves whenever a Bluetooth input device shows up.

I dont add output devices as I'm happy for that to flip between speakers/headphones - whatever is available.