It's a very strange thing, if I start my pc and directly go play warhammer 3. it runs like before. but if I play GTA5 or any other games then play warhammer 3, its grand campaign map runs only around 45 fps. I used to having around 60 fps before 6.2 update. but I found a solution for it, go enable windowed (or disable it),btw I have reinstalled NVIDIA driver and the game itself, doesn't help at all.
RTX2080super windows 11 32GB RAM SSD i9-9900k  1440k