Does anyone have my same problem? I’ve been noticing a small white square-shaped box appearing on the left of the screen whenever i press left mouse button. It only lasts for about 1 second even if i keep pressing lmb. I tried to analyse and repair the game from the launcher but it seems to be all right so i’m confused on why this is happening.
Hello Kevin95Death 
Please keep in mind that this is the Italian forum for Overwatch, and the expectation here is for posts to be written in Italian only. For your future reference, the English forums are available here.
As for your issue, the white square-shaped box you see when you press the left mouse button is a feature of the nVidia Reflex system. There is unfortunately no option at the moment to disable the effect in-game 
Oh, thank you anyway. I was suspicious on the nVidia stuff but i was not sure. By the way i wrote in english to have more visibility among the forum users but i’m italian so i’ll remember to use the same language as the forum i’m in if i’ll have any other troubles in future 