Yeah,
This is Apple's not too subtle way of making previous iPad owners to either upgrade their iOS software and/or purchase new compatible hardware to still be able to use Apple’s most recent versions of their apps.
And Apple does no longer make the older versions of their apps available for redownload, any longer.
Apple used to allow downloading of their older app versions, but no longer.
This is why I use this older version of iTunes ( version 12.6.5 ) as this version is still made compatible up to iOS 12 and iTunes 12.6.5 still saves the actual apps in iTunes from all of my iPads with older iOS versions.
If interested in this iTunes option,
iTunes 12.6.5 found here.
Deploy apps in a business environment with iTunes - Apple Support
iTunes 12.6.5 for the Mac requires OS X El Capitàn 10.11.4 or later. Not sure of Windows PC requirements on this version.
If you have already downloaded the recent 12.7/8/9.x versions of iTunes, you will need to find your current iTunes Library folder on your computer ( usually located in folder labelled Music ) and, temporarily, move/copy this folder to another location so you do not accidentally write over your existing current iTunes library.
To use an older iTunes version and once it is downloaded and installed on your computer, at launch, hold down the Opt/Alt key on your keyboard while launching this older iTunes version, so you can create a new Tunes library.
You may have to manually transfer data from your more recent iTunes library folder to the new one you created for iTunes 12.6.5, but not entirely sure.
This probably doesn't help you at this stage, but I wanted to let you know that Apple has provided another, less promoted, iTunes option to use that will still save and restore apps, in iTunes, like iTunes used to be able to do.
Best of Luck to You!
