Thank you for your reports on this. Microsoft is working to re-enable secure support for virtual camera apps on the Mac client. Until then, you can use the virtual camera in Teams in Chrome or Edge on your Mac.
We will update here and at the link below when there is more news: https://docs.microsoft.com/microsoftteams/troubleshoot/teams-on-mac/virtual-camera-doesnt-work-macos.
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May 7, 2021: Microsoft has still not sorted this out after 10 months. Why does it take so long to solve this simple issue?