This all sounds more like a problem with the software you're using than OBS
Try going into Chrome setting->Privacy and you should be able to select which sites can access which cameraI'm pulling my freaking hair out. Since installing OBS, default cam in Facebook Messenger calls (in Chrome) is OBS virtual camera, and the dropdown is greyed so cannot change back to my actual webcam. I don't even have OBS running!
I get the same dumb OBS virtual cam placeholder screen instead of my camera feed.
Chrome settings already changed to make native cam default, didn't work.
Uninstalling win-dshow didn't work.