How Total War: WARHAMMER III runs on the Radeon RX 580
Our estimate puts the Radeon RX 580 at about 40 fps on High at 1080p in Total War: WARHAMMER III, which means it runs acceptably. On Low the same card manages about 77 fps, and on Ultra about 29.
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: Low (about 77 fps); 1440p: under 60 fps at every preset, best is 55 fps on Low; 4K: under 60 fps at every preset, best is 31 fps on Low.