1. Right click the game on your library, go to Manage > Browse local files.
2. Find Z.exe on the folder and right click it, select Properties.
3. Go to Compatibility tab.
4. Click "Change high DPI settings".
5. At the bottom, enable on the checkbox for "Override high DPI scaling behavior. Scaling performed by:"
6. Leave it as "Application".
7. Click OK. OK again and close the windows.
8. Enjoy the game on proper resolution.