How Crusader Kings III runs on the Radeon RX 580
Our estimate puts the Radeon RX 580 at about 63 fps on High at 1080p in Crusader Kings III, which means it runs well. On Low the same card manages about 120 fps, and on Ultra about 45.
The graphics card is the limit here, so lowering the resolution or the quality preset is what raises your frame rate.
For a steady 60 fps, our estimate says: 1080p: High (about 63 fps); 1440p: Medium (about 64 fps); 4K: under 60 fps at every preset, best is 48 fps on Low.