Steam overlay reduces FPS in Warzone by 20-30fps - fix - turn off steam overlay
So I've been seeing online at how Battlenet performs better in Warzone than on Steam and though maybe they are just gimping the steam version. After several tests I found the reason - Steam overlay on whilst in-game. Automatically gave me a 20-30fps boost when I turned it off (must restart game if u do whilst in game).

Now that begs the question, how many games also suffer these performance losses with this setting?

The devs need to optimize this if they want us to use it cos I now have it permanently turned off if it causes that much performance loss.

So my suggestion is - please optimize the Steam Overlay and whilst you are at it, the recording too as I have that turned off and exclusively use Nvidia app (much less resource intensive too).