Why does this game run so poorly?

[Anbraxas]

I am not sure whats going on but it uses 100% of my GPU all the time, lags every time thor swings a hammer, and generally is unplayable I get around 80 FPS until a fight commonsense then drop to 4 or 5 FPS the entire fight.

amd ryzen 7
nvidia rtx 2060
16 gig rams