Its like a 5 hour job to get something that technically works and then a 10,000 hour job to get something that works flawlessly. The Apple integration with the iphone and macbook is the most seamless setup I've seen so far but I've still gone back to just using the built in webcam because its too fiddly to put my phone up on the screen and occasionally have issues where it won't connect.
Phone as webcam just doesn't seem like a long term solution, eventually built in webcams will be cheap and good enough. And tbh I find the built in one on the macbook to be bordering on good enough once you consider how compressed and tiny the output will be on the other persons screen.
MVP to full product is definitely the bigger part of the work. In the environment of early COVID, I think an app that had some rough edges would've still been very useful. Perfect is the enemy of good and all that. Phone as webcam shouldn't exist at all (how do you even mount it?), but somehow the video and audio quality on phones is still years ahead of what's available on even high-end laptops.
Rough edge apps have been around for years. I tried one that worked in the browser and could connect to OBS on your laptop, it was just too cumbersome though.
Apple actually did come up with a good solution for mounting the phone. A small disk that connects to the iphone with magsafe and has a flip out tab that can hook on to the top of the macbook. It's surprisingly stable and nice.
I had the opposite experience. I have a personal iPhone and a work iPhone and every time my work iPhone is near my work computer, it switches to it whether I want it to or not. It drives me nuts. It's fine when I want to initiate it but the number of times I've just set my work phone down on my desk thoughtlessly and then tried to start a video meeting in Slack or Teams or Zoom only to not have video because it's using the camera pointing at my desk is too many.
Phone as webcam just doesn't seem like a long term solution, eventually built in webcams will be cheap and good enough. And tbh I find the built in one on the macbook to be bordering on good enough once you consider how compressed and tiny the output will be on the other persons screen.