iPad does not do automatic screen rotation
Is rotation lock on? Open Control Center by swiping from the top right of the screen (iOS 12+), then tap the rotation lock icon on the top row.

If you see  in the status bar, Orientation Lock is on. To turn it off, swipe up from the bottom of the screen to open the Control Center, then tap .
If you have an iPad with a Side Switch and don't see the Rotation Lock icon in Control Center, make sure that the Side Switch is off.

If the screen doesn‘t rotate on your iPhone, iPad, or iPod touch