This is happening to a lot of users right now, it seems to be an issue with Apple computers in general and camera use within the browser. There are some things you can do that will hopefully solve the issue.
First and probably the easiest, try using Firefox... this seems to be the browser least likely to be affected by issues right now involving camera use.
Second, make sure you don't have any strange extensions installed in your browser or in particular make sure you don't have the "Grid" extension installed. Here are instructions for checking and uninstalling extensions on the three major browser available for MacOS:
https://www.howtogeek.com/240090/how-to-uninstall-extensions-in-chrome-firefox-and-other-browsers/
Third, if neither of the above does the trick you can disable hardware acceleration which also can help quite a bit.
Instructions for Chrome:
https://www.howtogeek.com/412738/how-to-turn-hardware-acceleration-on-and-off-in-chrome/
Instructions for Firefox:
https://support.mozilla.org/en-US/kb/hardware-acceleration-and-windowblinds-crash
Finally, the issue can be linked to certain versions of MacOS so make sure that your computer is fully up to date. You can do this by beginning with step 4 of the article listed below:
https://support.apple.com/en-us/HT201475
Let us know how it goes, thanks!