Ya I've given up waiting around for gpu encode/decode AV1 in dvdfab. I've upgraded my secondary gpu to the intel arc a770. the acer bifrost version. it was on sale for $330 awhile back.
works phenomenally well in handbrake. 1080 content gets around 330fps in 10bit encodes. about 150fps in 4k encodes.
also if you want to take a look the program FastFlix does nvidia av1 encoding now, it's also a free program