This has been happening to me as well since mid-Dec on my MacBook Pro (13-inch, 2020, Four Thunderbolt 3 ports) running macOS Monterey 12.6. Teams version is 1.5.00.33356. Yes I have an external USB camera (logitec) and the jitter / phantom re-appearing key frame issue happens on the second monitor.
This makes Teams for videoconferencing unusable and I hope it gets fixed very soon. Videoconferencing in-browser does solve the video glitching however even that has become completely unstable for some reason and I get bounced out of meetings after a few minutes. I've had to convert meetings over to Google Hangouts or Zoom as a result, and seeing how those all work perfectly fine (as did Teams prior to mid-Dec) leads me to believe that this is a 100% Teams issue.
I could be totally wrong, but this does look like a key/i frame (delayed) retransmission issue. I don't see any pixelation so delta frames are working as they should but it's like the next time an i-frame should be displayed on a second monitor, Teams is picking one out of the buffer that is the previous one and not the current. Another thing to note is that this is only affecting the display of all videos and my camera feed, but to all other participants my video seems normal.