Like Khorvoc said there is a huge forum about this issues.
It’s a wow issue…
This forum may explain some of what you’re experiencing with the fps issue and stuttering.
There is a blue asking for dxdiag so the devs can get samples to find the issue.
https://us.forums.blizzard.com/en/wow/t/massive-stutters-with-df-client/1379249/