With ffmpeg 5 using libaom it's actually reasonable. Obviously it depends on quality and whatnot, but I'm able to get about .25X of realtime playback speed with AV1 encoding. The magic switch is setting -cpu-used to something higher than the default of 1, which is go-on-vacation-and-maybe-it-will-finish slow.
Rough example: `ffmpeg -i video.mkv -c:v libaom-av1 -cpu-used 5 av1_test.mkv`