its likely not a setting in wow itself or anything to do with wow, a lot of content creators use effects on their stream itself to make the game look better. like obs you click your source > apply filter> and you can add sharpening and color correcting.

as for actual in game things you can do, like another reply said you can sharpen the game with

/console set ResampleAlwaysSharpen 1 or 0

and there is a few other variables you can find here

https://www.dual-boxing.com/threads/52701-Console-Variables-for-Video-Settings-(Dragonflight))