Update: I decided to give last Chromium 122.0.6261.69 a try, and to my surprise, the JS Fiddle returns the same successful output as Chrome, which should mean that H264 is working again 
(I haven’t been able to test it with MS Teams yet)
So, for the time being, I’ll mark this as solved. I’ll still wait for concrete confirmation before marking issue 2264332 as closed, though, just to be on the safe side.
Thanks to all that participated! 