I saw someone posted the same issue over in the US forums so glad I’m not alone.
Sometimes - not EVERY time - when I tab back to WoW from a browser, the entire game freezes as if its crashed. But if I wait, after a while, the world re-renders (sky then ground then assets then characters) and is fine.
i9 13900K
RTX4090
(Latest drivers/bios updates for both)
32GB RAM
its about windows 11. today new update released win11. hope it fixed. didnt tryed even.
Hey does this happen on browser if there no website loaded in as well or web page without any video playback including paused video playback ? this includes gif as well.
If this freeze happens when you have Google chrome open, try to go to google chrome and turn off the option “Use graphics acceleration when available”. It fixed it for me 
I had a win 11 update on friday, and so far my PC has not been spazzing out when I tab out.