ähmm… You own a 4K monitor, but choose WQHD as resolution ? Thats not optimal in terms of quality, because not exactly scalable. Then better choose native resolution and lower the renderscale. Or, then you can use DLSS, which is made for exact that reason 
( think thats what you mean in the “edit” )
I’am not sure whether devs can change the DLSS factors, thought these are fixed values which game developers can not change 
You can of course combine DSR and DLSS… , but then of course with a 4K monitor the main resolution in windows needs to be changed.