Well, the graphics in Civ 6 are kind of secondary. You want a lot of CPU to help with calculating AI moves each turn to speed up gameplay. 2080 Super is more than enough for the graphics.
GTA5 is getting kind of old, most quad cores can handle it just fine. Even old high end dual cores can get 50FPS.
Borderlands 3, Unreal Engine, again, most quad cores are adequate.
If you are planning for 4K, then CPU isn't super important for graphics heavy titles. Really depends on what you want to spend.
Common recommendation for a high end CPU would be the Ryzen 3700X. 8 cores 16 threads, relatively cheap motherboards.
If you want absolute maximum frame rates possible, Intel is still the way to go. 9900k will set you back a bit, high end motherboards, mandatory CPU cooler purchase. An overclocked 9700k will get you about 95% the same FPS. Intel has announced 10th gen CPUs, Z490 boards are not going to be cheap, But they are now offering up to 10 cores on the platform (AMD offers 12 and 16. FYI) So the 10700k might a little cheaper, or about the same as a 9900k both in price and performance.