Change resolution to 1920 x 1080

[BigGTnT]

Anyway of making this full screen, no black vertical borders, tried manually configuration in file management, but you still have left and right black bars, resolution change only zooms into map.

[Torchfire]

That makes me wonder if I had black bars when I played earlier...

It's just not something that most people even notice.

[Zoltan Redbeard]

You can get the software Lossless Scaling here on Steam and set it up quite easily to run the game at the desired resolution without black bars. It's probably possible to do that with QualityScaler too, but I personally haven't ever tried it.
Both softwares aren't free, but at least the first one does what it's supposed to do pretty well.

[Enen]

There are different guides to fix this. What worked for me is downloading a 3rd party software. CnCNet and you can fix it(menu is still with black borders but ingame you are zoomed out and no black bars).

I also saw a guide with no 3rd party software where you go into the game files and change it manually(you can open it with notepad) and some people type "hires" in the menu. But I recomment CnCNet. Easy to install