A "fun" thing here is that it isn't possible to create or open these streams in ffmpeg due to neither hevc or AV1 being part of the Adobe RTMP standard. At least as per this thread:
The hardline opposition to adding hevc etc support to rtmp came from ffmpeg+gstreamer afaik, and from the document it looks like at least ffmpeg is on board.
...Might have to brush off our broadcast software and add this :)