When I choose full screen with the Site Designer app, the program itself exceed the display properties. About 25% of the menu is off the screen at any time. If I drag the title bar across the screen, I can see the remaining menu. Weird behaviour. I thought windows programs aligned themselves with the reported display properties of the devise they are operating on. I am using a laptop with display set to 1920 X 1080.

Check the settings of your monitor. Right-click on an empty spot on the screen and choose settings. You should find something that looks like what I'm attaching, about the display's resolution and size. I only have a Norwegian version of Windows, but you should be able to find the settings shown in the screenshot. Make the values the same as mine.