Just add a workflow to the element. When an element is clicked, Go Fullscreen action to be activated int eh workflow.
Actions:
Go Full screen: Takes the screen full screen
Exit Full Screen: Exits the full screen
Toggle Full screen: Full screen toggles using the same button for going full screen and exiting full screen.
Element:
Fullscreen Detector: Detects whether the website is in fullscreen on the browser.
Auto Fullscreen Trigger: When this element is placed in the page, the page automatically asks user to enter full screen on page load.
Demo app editor:
https://bubble.io/page?id=fullscreen-demo&tab=Design&name=indexDemo App Link:
https://fullscreen-demo.bubbleapps.io/version-test/?debug_mode=true&view=Home