Former film student here, this is all correct but I wanted to rephrase part of it-
Most of the time, you don't need to worry about focal length ( especially because it's so complicated when you're trying to talk about different sensor sizes)
The real measurement here is distance from the camera. The further you are physically from the camera, the flatter things look. Now, when you're further away, you obviously need to zoom in to make your head fill the frame, but it's way easier to think about it in terms of distance first, and then find a webcam/lens/crop that works.
I use a pro camera as a webcam (with a cheap HDMI/USB stick), and I have it mounted on my desk around 3/4 feet from my face. That seems to work well for my face shape.