iPad Pro Microsoft OneNote: How to get more space below?
I am able to use the down arrow for hundreds of repetitions to keep scrolling empty content in my OneDrive backed notebooks. The physical keyboard is faster, and I’ve tested Bluetooth and hardware connected keyboards. Also, two finger zoom (pinch and expand) and tapping lets me add new text boxes anywhere.

I wonder if you don’t have an O365 license and activated the product or there’s some other difference between my setup and yours, but this has never been an issue for me the last 18 months using the iOS OneNote app on iPhone or iPad.

Version 16.36 (20040600)
iPadOS 13.4.1
Enterprise E3 and E4 O365 licenses tested

Lastly, the in app feedback is really good imo - in many ways better than AppleCare and in some ways worse. Have you tried vendor support to be sure there’s not a setting or FAQ/Guide that covers this?