How to Turn Screen Rotation On / Off - Samsung Galaxy Note9
3D Accelerometer Rotation is a feature that allows flexibility in how the content is viewed on the screen. Simply turn the device from vertical to horizontal (or horizontal to vertical). The device senses the change in orientation and automatically adjusts to fit the screen.
Camera, album, music player, videos, web browser and many other apps take advantage of this feature.
Swipe down on the Status bar (at the top).
The image below is an example.
Swipe down from the top of the display to expand the quick settings menu.
Tap 'Auto rotate' or 'Portrait'.
When Auto rotate is selected, the icon is blue. When Portrait is selected, the icon is grey.