Big Business is not designed to run in Full-Screen mode on macOS. Most windows are forms which work better taller, but blow up when made too wide. If you accidentally click Full-Screen, you can hit the ESC Key to escape.
The annoying thing about Full-Screen is controls disappear. There is a moment of panic when there is nothing on your screen except form. No menus, Apple or otherwise. No Close Window button. But there is an escape, using the esc key in the upper left of your keyboard.