there are a number of youtube videos about boosting FPS for Valheim. I did a bunch of stuff and out in the world i get about 100fps, and about 70-80 near my building projects. It goes down to about 60 in my portal hub. all at 1080p full screen. GTX 1060 6gb Ryzen 5 1600.
I'm not a hardware expert by any means but I feel like your setup should be crushing this game at 1440 even on max settings. but again, i'm no expert.
do you have GeForce experience? are your drivers up to date?