Can't run CS:GO at fullscreen (Ubuntu 18.10)

Solution 1:

1. Open Steam
2. Go to the "Library"
3. Right-click the game which needs to be reconfigured
4. Select "Properties" from the menu
5. Click the "Set launch options..." button
6. type: -full and save

That's all.

Solution 2:

I just faced a similar problem. In my case, the initial window height was too big, so that part of the lower UI was cut off, including the "Apply Changes" button.

I had to set a smaller height in the game's launch options (-h 700 for my 1366x768 screen). Aftwards I could switch to fullscreen in the video settings. After removing the launch options again, the game now starts in fullscreen mode.

Hope this helps!

Solution 3:

Kind of an alternative and unresourceful answer, but I used the Rotation Lock (2nd icon in image) to change my screen to portrait mode, change settings accordingly, and then back to landscape.