iPadOS 13 was the first iteration of the OS, and iPadOS 18 is the latest.
Get the details about each version.
iPadOS 19: Whole New UI?

iPad running iPadOS 18.Apple Inc.
iPadOS 18 brings the Calculator app to the iPad.
It includes Math Notes, which lets you solve equations by writing them out.
Another new app with this interaction of the operating system is Passwords.

Apple Inc.
The last major update is with the widgets that already appeared on the iPhone in iOS 16.
Similarly, you have two minutes to un-send a text you’ve sent by mistake.
Tab groups have also received an overhaul.

Apple
They’ll update automatically as people add to or subtract from the group.
In addition, enhanced widget options allow users to place widgets with apps on their Home screens.
Users can also enter the App Library from the Doc to effortlessly access and organize apps.

Apple
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This version of iPadOS featured several refinements to the interface, redesigned apps, and augmented reality.
Apps were enhanced with sidebars and pull-down menus for easier navigation.
Finally, cycling directions and electric vehicle routing were conveniently added to Maps.

This version also added improvements to Slide Over and Split View.
iPadOS 13 introduced improvements to Apples fancy stylus, the Apple Pencil.
iPadOS 13 added a few more gestures, specifically tailored to text editing.

Users could use the three-finger pinch to copy, three-finger spread to paste, and three-finger swipe to undo.
Double three-finger pinch and you couldcut text just as easily.
This was a fantastic addition for users of web apps like Google Docs or WordPress.

The much-anticipated Dark Mode arrived in iPadOS 13, and not just for inverting colors.
It was created from the ground up and integrated across the whole system.

Apple Inc