AV1 decode is supported on the RTX 3000 series, encode + decode in the RTX 4000 series
For Intel Arc, AV1 encode + decode support is present on all Arc Alchemist GPUs,
For AMD, AV1 decode is on RX 6000 series, encode + decode on all RX 7000 series GPUs
As someone else has recommended, a low end Intel Arc alchemist GPU is pretty great for stuff like Jellyfin, very low price to entry for gfx accelerated AV1 transcoding.