How do you get out of Full Screen mode in Excel? No red or yellow buttons visible.

Have you tried control+command+F key combination. That is usually a toggle between full-screen, and normal application windows.

Move your mouse pointer to the top and the menu bar will be visible.

Click on the green button to get exit full screen.

I Don't think Microsoft updated it for those buttons. Look for a blue button with arrows in it on the right side of the menu bar.

Also try Esc key.