This picture makes me a bit envious now. I wonder what your frame rates are like, with landscapes like this, but more so with settlements...
The next consideration would be: I have a graphics card (RTX 3070) that should be suitable for 4k, but would "only" need a new monitor (mine only has 1440p).
If I could only estimate what frame rates I could expect (I don't overclock).
Not seeing what your comment has to do with taking high res screenies in open but there's nothing stopping you from running at a higher game resolution (either with DSR in the Nvidia control panel or using one of the in-game scaling options) to see what your framerate will be at any resolution.
If you just want to be able to take really high quality screenshots the framerate the game can run at that resolution doesn't really matter.
Using DSR 4x, I can change the screen resolution to 7680x4320 (the game runs at about 15fps at this resolution on my PC) and in solo, use alt-f10 to capture a high-res screenshot. It takes maybe 5 secs to generate the image, the final pic is captured at 15360x8640, the bitmap file is 379Mb.