iPad Air 2 (2014) cannot backup

My father still owns an iPad Air 2 from 2014 that’s still working. Battery is dying though, jumping from 100% to 20% in a second and switching off.

He uses his iPad every day to read emails, news, watch videos and basic stuffs. He does not want to spend money on any new or refurbished iPad. His wish is to transfer data to an older iPad 4. I know this is crazy.

I have tried backing up the iPad Air 2 via USB / iTunes (he has a 2011 MacBook Pro). iTunes only gives the option to erase or restore from backup. No backup is possible.

Last backup was in 2017.

I have tried backing up via iCloud: with the tablet charging, even though the process goes through, no backup is created. Not even a warning.

Last resort, I have tried migrating directly on the iPad 4 by logging on n to his Apple ID account. While the procedure seems to be working, when it is time to confirm a new device via another one (iPad Air 2 in this case), the confirmation is displayed too late and the process never ends well.

What can I do?