New iPad Mini No Slide switch - so how to enable screen rotation everything in landscape now

Swipe down down from the upper right corner of the iPad's screen to reveal the new location of the iOS Control Panel

Tap on the red rotation lock icon with a circular arrow with a padlock image inside of the circle.

Best of Luck to You!

Lots have change in iOS 12.

iPad User Guide for iOS 12.3 by Apple Inc.

https://books.apple.com/us/book/ipad-user-guide-for-ios-12-3/id1420662722