IPA stands for iOS App Store Package, which is a file format used to distribute iOS apps. Facebook IPA is the package file for the Facebook app, which can be downloaded and installed on iOS devices. By downloading the Facebook IPA file, you can install the app on your device without having to access the App Store.
Downloading and running the Facebook app on is a common challenge for users of legacy devices like the iPhone 4, as the official App Store version now requires iOS 13.4 or later . Current Status & Compatibility
If you still want to try, here are the typical sources where legacy IPAs are archived. Downloading IPAs from third-party sites is risky. Files may contain malware, trackers, or stolen credentials.