Remove this option from device

Thanks for the additional information and the screenshot. Based on what you've shared, the fullscreen button shown in the bottom-right corner appears to be a Samsung or device feature rather than an FC Mobile feature. Unfortunately, we can't remove or change device-specific overlays from within the game.

You may want to check your phone's Game Booster or Game Launcher settings or other display-related settings to see if this overlay can be disabled. If you're unable to find the option, Samsung Support should be able to advise you on how to turn it off on your Galaxy A05.