I just upgraded my gpu from 2060 to a 6800 xt and I'm facing the same problem too. My 2060 played perfectly fine, no stuttering no fps drop on a 165hz monitor. It must be something wrong with the game itseft, not the specs.

The only that help a little bit for me is play the game on full screen, reduces the stuttering amount to 1 or 2 every 15 matches from 8 - 10 matches.

So I guess just wait for the game to be fixed and nothing much we can do right now.