Running Facebook on iOS 9.3.5 (standard for devices like the iPad Mini 1 or iPhone 4s) is a challenge because the modern Facebook app requires iOS 13.4 or later. To get it working, you generally need to rely on "Legacy" methods or the device's App Store history. Options for iOS 9.3.5
I should warn the user about the risks of using an unsupported iOS version and an outdated app. They might face security risks, no updates, and possible app incompatibilities. If they’re doing this for compatibility reasons, like an old device (like the iPhone 5c or 5s), maybe suggest alternatives, like using an emulator on an Android device or a computer. Alternatively, check if Facebook has an archive for older versions, but that’s unlikely. Companies usually don’t keep old versions around. facebook ipa for ios 935
Since the App Store no longer serves these versions, the IPA must be sideloaded. Running Facebook on iOS 9