Considering your specs you shall have 60 fps at 1440p, with high settings and some on ultra, in countryside areas. It’s what I had with the same proc and rtx 2080 (now I changed my pc).
What is your vr setup (headset and middleware to access VR)? Is your vr setup launched when you play flat screen? I suspect your issue came after you played in the vr mode maybe with smoothing techniques activated (that divides the fps by 2) and can be cpu costly. Somehow maybe this has an impact on flat screen mode also. This is a theory.