This happened to me, so I am going to explain my process for getting out of fullscreen. What you need to do is temporarily change the scale/layout of your computer. Go into settings and find the layout, next to the display and resolution settings. Decrease the percentage. Use one of the presets, do not do a custom one. Open this app and change the mode to windowed. Then move the window and shrink it down. Then return to your normal preset. and Use the app as desired. Alternatively you can stay inside fullscreen mode and use the application while your scale is altered returning it to normal after you are done using the game.
