Unfortunately, what you are attempting to achieve simply isn't possible. Some explanation may be helpful...
1) Rolling-back to an earlier version of iOS/iPadOS is not possible.
All System Updates are digitally signed by Apple - and can only be installed whilst the digital signatures remain valid. After release of a new iOS/iPadOS version, the immediately preceding version continues to be digitally signed by Apple - however, usually within a few days, Apple will revoke the digital certificate with which the earlier version is signed.
2) Your iPad with iOS 10.3.3 installed is an iPad4. The iPad has a 32-bit system architecture - unlike current models that have 64-bit architectures.
App Developers have dropped all support for 32-bit devices and many for iOS versions preceding iOS11/12/13 - and have withdrawn older versions of their Apps from the Apple App Store. Withdrawal of Apps supporting older models of iPad is making their utility and usefulness significantly more limited. Once compatible versions Apps are withdrawn, you’ll not be able (re)download or (re)install them.
3) Apps cannot be directly transferred between devices. Similarly, while App data can be restored from a backup, Apps themselves and the installed OS are not included within an iCloud or iTunes backup.
Instead, Apps can be downloaded and installed on other devices that are signed-in to the App Store with same AppleID - but only if the App is compatible with the iPad and remains available for download.
In conclusion, you should now have a good understanding of the multiple factors that prevent what you hope to achieve.
