Maybe you're in need of an iPadOS 13 sub-forum even more then, since there are several other differences. Actually, I think Apple should have separated iPadOS out years ago, but iPadOS 13 goes much further.
Sidecar
Multitasking update <-- Very different. I'm still trying to wrap my head around this. Big learning curve.
Dock (similar to iOS 12 but nonetheless a huge difference from iOS 13)
Notifications
Expose
Desktop Safari
Home screen widgets
Apple Pencil improvements (as a part of ProMotion, which doesn't even exist on the iPhone or iPod)
Apple Pencil screenshots
Markup tool palette interface
Mouse and trackpad support <-- This works on iOS 13, but is kinda pointless there.
Shrinkable keyboard that floats
Files app interface differences
USB-C support and compatibility with external devices
Some of the above are partially hardware dependent, but nonetheless they highlight the differences between iPadOS 13 and iOS 13.