Get a cheap Intel ARC A310 card. I have one in my workstation along side my AMD GPU purely for streaming/encoding. It works great.
Also, OBS handles AV1 nicely, but you can’t stream to a site like Twitch because they only support H264 outside of specific experiments.
That said, Arc GPUs are nice, I have an A580 and while the drivers aren’t as mature as Nvidia or AMD, I got it for a pretty good price and they’re gradually patching things out.