Hey,
I have isuue with periodically fps drop from normal to 20-50% normal fps, usually from 80 (I have set max fps in settings, because I have only 60Hz 4K monitor) to 25-50 fps so then is lags and tearing in game and it is unplayable for me.
I try turn off browser hardware acceleration but that dont help. Then I read advice on one forum, so I turned off Battlenet completely, it goes fine couple of hours, but after 1day it lags again.
I bought new PC special for Diablo4 but it seems be worthless.
I have i7 13700KF CPU with 32GB DDR5 RAM with Gainward Phantom RTX4080, game is installed on M2.SSD disk, I get all drivers updated, no problem in others games.
Playing D4 on max details offcourse.