I bought a new monitor recently and I have been having an issue with both WoW Classic and Retail WoW where I will get 2-3 seconds of black screen when alt tabbing.
I am playing both in windowed (full screen) and the resolution matches that of the desktop.
I have since fixed the issue with WoW retail by changing from DirectX 12 to DirectX 11.
The issue with WoW classic persists as there is no option in game to swap which version of DirectX you are using. I have tried adding ‘-d3d11’ as an additional command line argument, as well as adding ‘SET gxApi “d3d11”’ to the config file; neither seems to have fixed it.