Installing the Facebook app on iOS 9.3.5 is possible through legacy compatibility features or jailbreaking, though the official current version is not compatible as it requires iOS 13.4 or later. Method 1: Native "Last Compatible Version" (No Jailbreak)
If you have never "purchased" Facebook on your account, the App Store will simply tell you the app is incompatible. You can fix this by using a newer iPhone or iPad: Old iPad version 9.3.5 app download issues - Facebook facebook ipa for ios 935
Open Cydia , search for, and install a tweak called "Checkmate, Store!" . Installing the Facebook app on iOS 9
Instead of fighting the iOS 9.3.5 limitations, consider these practical alternatives that preserve your battery and sanity. Instead of fighting the iOS 9
iOS 9.3.5 devices have limited RAM (often 512MB to 1GB). The Facebook app is notoriously resource-heavy, leading to long load times and frequent crashes.