Hi,
go to the folder: Library/CoreMediaIO/Plug-ins/DAL.
If you didn't plan to use OBS's Virtualcam but want to keep the software, delete the Virtual Camera from there. Keep in mind that every time you activate it (from OBS) the necessary file to make it work will be reinstalled.
ABout changing the camera or microphone, you won’t be able to change the default webcam and microphone for WhatsApp unless you place a call.
Ciao.