Depending on which hardware you run, please try the following:

Intel:

* Intel Control panel and switch the 'Scaling' option from "Maintain Display Scaling" to "Maintain Aspect Ratio"

Nvidia:

* Nvidia Control Panel. Change "Aspect ratio" to "No scaling" on the Adjust desktop size and position page (with "perform scaling on Display")

AMD:

* AMD Radeon settings and under "Display" change scaling mode from "preserve aspect ratio" to "full panel"

This can also occur when your PC doesn’t meet minimum requirements.