If you previously "purchased" an app on a newer device using the same Apple ID, you can often download it directly: Open the on your iOS 9.3.5 device. Go to the Purchased tab.
Ultimately, the search for a "free IPA library" is a symptom of a larger issue regarding the "Right to Repair" and the planned obsolescence of technology. Users resort to these unofficial libraries because the official channels have failed them. When a perfectly functional iPad is rendered useless not by hardware failure, but by software incompatibility, users are driven to alternative methods to maintain the value of their purchase. ipa+library+ios+935+free