Sorry, it's not hardware. Spent hours trying to resolve this issue and being told to reset xy&z doesn't work - neither does safe mode/new account... check this is a parallel discussion on the issue: https://discussions.apple.com/thread/251186757?answerId=252724128022
This issue is well know to Apple: last update 10.15.5 includes" Resolves an issue where the built-in camera may not be detected when trying to use it after using a video conferencing app" but it's far from resolved.
It's affecting built-in cameras on both new and old MBPs, as well as 3rd party webcams. It appeared with the intro of Catalina, and right now, if you have a Mac that has 'lost camera', forget video conferencing at the moment. There is nothing wrong with your USB ports - for sure all work perfectly with anything else plugged in, and there is nothing wrong with the external cameras - bet they work fine on Windows and anything pre Catalina!
I have 4 minis, server, 2 IPh11 +++ / Mbp 2012+2015 / 3 ipads / 5 windows10pcs +++ on my network ... and have been an apple customer for over 30 years. I've given up trying to fix it, now checking discussions so you don't waste your time!
My fix - thanks to link above, duped my mpbs back into Mojave, time machined them to feb - before the issue started to become apparent - have current work on minis, on network, so can access on mbp. It's ugly,but it works