Simple solution for fullscreen issue on Windows 10

[CthulhuCultist]

I can't say if this will work for everybody, but it worked for me.

Right-click on the .exe file
Choose 'Properties'
Choose 'Compatibility'
Click 'Change high DPI settings'
Check the box 'Override high DPI scaling behavior'
Make sure the dropdown menu says 'Application'
Hit 'OK' and run the game as you normally would.

No more black bars!

[Jotamide]

Thank you so much for this. It worked for me as well!