AMD RX 570
The AMD RX 570 is a budget video card from AMD. It's fine for 1080p on GNU/Linux and can even be used for a 3x4k monitor setup if you're content with playing games on medium/low settings.
Video encoding and decoding
AMD Polaris cards like the RX 570 can't decode or encode VP9.
It is possible to encode H264 and HEVC video with this card using ffmpeg and software like OBS using VAAPI. The limitation for using hardware encoding with VAAPI is quite low at 1080p30fps. You will not be able to hardware encode 1080p60 video or 1440p even though the card actually does support much higher resolutions, see https://github.com/obsproject/obs-amd-encoder/wiki/Hardware-VCE3.4 for an overview.