Just found this thread. Graphics have been freezing for me on Civ 6 on new 2020 iMac with 32 gigs of ram and AMD Radeon Pro 5500 XT (8 gigs VRAM). I started a new game with no mods installed, yet it keeps happening. Running macOS 10.15.7. I've submitted a report to Aspyr. Not sure if my issue is that same as yours. The sound still plays, and I can click and hear responses from units, etc., but get no visual representation of what I'm doing. Can't even force quit, the image on the screen starts tearing apart.