default camera and microphone

I use my MacBook Pro M1 closed with a separate monitor. I also have a Logitech webcam for using with zoom meetings. So I start a meeting and the default camera & microphone is the Logitech, but after a few minutes both cutout and Zoom tries to use the MBP camera & mic. But of course the laptop is closed. Doesn't matter how many times I set the Logitech to be the camera it does not stick. However, and this is where it gets strange, if I have my iPhone nearby, I can select that camera & mic and it will stay there all the time.