Notes:
As of end-March 2022, checkra1n still didn't fix this issue / release a new update, so this method still works. Soon, I will be making a new guide (with pictures) on how to use this script as it was complicated for many people.
Requirements:
- iPad Pro 9.7-inch (2016) or iPad Pro 12.9-inch (2015) with iOS 14.5 or higher
- checkra1n.app installed & located in the Applications folder, if it's not there, move it to there or change the path in the script
How to use this script:
Download the file "PongoConsolidated.bin" from this link: https://github.com/checkra1n/BugTracker/files/6429930/Pongo.zip
Extract it.
Navigate to /Applications/checkra1n.app/Contents
Create a new folder named "A9X" inside it.
Put the file "PongoConsolidated.bin" into the A9X folder.
Run the script.
Plug in the iPad, in Options mark "Allow untested iOS/iPadOS/tvOS versions".
Jailbreak your A9X device.