In mobile browsers like Opera, achieving fullscreen mode is typically done through gestures or options within the browser interface, as there are no traditional keyboard shortcuts like on a desktop.

Here's how you can activate fullscreen mode in Opera on your mobile device:
Open O

Opera and go to the webpage you want to view in fullscreen.

Tap on the Opera icon (O) to access the menu.

Tap on the Opera icon (O) to access the menu.

Look for an option related to fullscreen or immersive mode.