As far as I am aware, there isn’t any hw suppport for av1 in plex. It would need support in ffmpeg and then for any of those changes to propagate up through plex’s custom version of it.
Aside from that, there are limited support for av1 in video cards themselves (and yes I am aware that the n100 can support av1 decode), but of course that will increase over time.
no AV1 support listed @ https://support.plex.tv/articles/115002178853-using-hardware-accelerated-streaming/
hmm, this closed feature request seems to indicate it may be supported on some things @ [Implemented] Add support for av1 coding standard - #365 by anon18523487
