Old post, but I found it, so I’m leaving this comment for posterity in case other people have similar issues and find this thread:
The reason it works on Borderless Window (but not Fullscreen) is because V-Sync and G-Sync only apply for Fullscreen (which could also be why some people may still get screen tearing on other applications or their desktop even with V-sync or G-sync enabled). If G-Sync is the issue, then that’s 100% why the game works on Borderless Window and doesn’t work on Fullscreen.
As a workaround, you can either try running the game in borderless window (if your CPU is strong enough and you’re fine with how it looks compared to fullscreen) or - try this first, actually - navigate to Program Settings, (just in case) uncheck “Show only programs found on this computer” (because it’s hilariously unreliable), find Overwatch, and disable G-sync this way.
This disables G-Sync only for Overwatch. You will not have to manually disable and reenable G-Sync every time you want to play another game, as this creates a setting unique to Overwatch that can’t be overridden by your Global Settings.
P.S. Hi, this is my first forum post ever (that I can remember, anyway). I’ve never even liked/interacted with any posts before. I’m brand new. I don’t know the common forum etiquette at all, so hopefully my comment is coherent enough and in the right location for what it was intended for.
P.P.S. Oh, also, if you’re a Nvidia GPU user on Fullscreen noticing screen tearing, never ever EVER use OW’s V-sync option in the video settings. It creates a horrible input delay. Instead, either play on Borderless Window or, if you absolutely have to play on Fullscreen, here’s the fix:
Open Nvidia Control Panel, navigate to your Global Settings (or Program Settings for Overwatch), and enable V-sync on “Fast” for the lowest possible input delay. You won’t even notice a delay and it will fix the screen tearing. (Personally, with my niche setup nowadays, I play on Borderless Window for instant alt-tabbing, among other reasons/fixes for other issues.)