for the people saying fps is better , they probably cant afford 4k equipment. i have a 4k 144hz monitor and you only need those high hz for first person shooters (70fps+).... anyways.
i am running full detail even HDR in 4K (predator 27 inch hdr 4k 144hz gsync).
my system is ryzen 9 3900x (corsair 115i cooler), 32GB gskill 3000 (4X8GB) running at 3200, a bunch of SSD's and evga 2080 ti ftw3 ultra hybrid cooled. i am steady around 670-80fps/hz on the highest settings, for sure i can use another video card with the same spec to run this game at 144hz, but you dont need high hz for this game. over 60fps is great. whats really important is having ALL THE 30+ SETTINGS AT MAX SETTINGS omg its so nice. the nicest looking game ever. holy smokes.......ppl with 1080 or 1440 CANNOT see what you see with 4k max settings.

dont understand why people would rather have the best possible graphics over fps, whats the point of the game looking good if the fps is trash?

just be smart and buy 1440 by 3440 with my i9 and 2080ti i get a solid 50 fps. lol, lets go !

the culprit is the volumetrics quality which squeeze a lot of power of gpus, just like in the assassins creed odyssey. i recommend to set it to medium or even low

meh 4k is a waste of time, I have a LG b9 OLED and I much prefer just playing at 2560x1440 and keeping fps at 100+ and no evena 2080ti will no run a stable 60fps at 4k on RDR2, I know because its what im running. Thus just run 1440p higher hz for better gameplay and your eyes and eyestrain will thank you.

lower water physics quality to 50, you won't notice much of a difference but your GPU will thank you

the RAGE [rockstar advanced game engine] engine, which is what this game runs on, has a decent scaling algorithm, I would recommend setting your render scale to 1/2 aka 0.5 and then changing your settings to reach your desired framerate, then from there work up each value for scaling and change settings to see how far you can push the core quality settings... I reckon you should be able to get 0.7~ render @ 4K with decent quality settings and 60fps. Even tho my card a 1080ti is similar when it comes to the stats of a 2080s, the 2080s does have better and newer optimisations which help it alot in more games. I currently use 0.5 render scale @ 4K with mostly Ultra except water quality with 60fps everywhere including Horseshoe Overlook