iOS 9.3.5 is famous for two reasons:
Modern versions of Facebook require iOS 13.4 or later. When you try to download it from the App Store on iOS 9.3.5, you often get an error saying the app is incompatible, or you're prompted to download the "last compatible version," which sometimes fails to log in due to outdated API protocols. facebook+ipa+for+ios+935+best
Some users have success using older versions of iTunes (v12.6.5) on a PC, which still includes the App Store, to "buy" the app and add it to their account history. The IPA & Jailbreak Alternative which still includes the App Store