From experimentation I observe that opera does auto-connect to any chromium-ffmpeg slot, regardless of whether it is new or not, and there has not been an auto-connection request from Opera (and certainly not from me on chromium-ffmpeg either) to auto-connect those new slots — the last one I found was in 2019.
@alexmurray, do you understand what is going on? Why would these repeated auto-connection requests be needed for Vivaldi but not for Opera?