When I tried to run ML2Scratch on a Raspberry Pi 4, there was a USB camera that didn't work. In conclusion, WebRTC on RPi4 with Buster doesn't seem to work with Logitech c270. And since it looks like an old camera, I don't feel like it will work with WebRTC for the time being. As a temporary workaround, I'm using another camera.
The results I have tried are as follows.
I threw it on the Raspberry Pi Forum (2020/3/18). It seems that there are quite a lot of problems, so I feel like I'm left alone. I'd like to find out if I have time, but unfortunately I'm pending because I don't have time.
The device can be checked with Linux commands and Chrome. For Linux, you can see it with the following command.
List of working drivers
$ lsmod -v
With Chrome, you can check the status of the media below. However, it is commonly recognized.
Check out the list of volunteer cameras running on the Raspberry Pi. Logitech C270 seems to have some compatibility issues and sometimes doesn't work.
Finally, take a look at Chromium's fault list. It doesn't look like Chromium's 74-78 corrections have been included here.