This is the "million-dollar question." Even if you successfully install a Facebook old version IPA, it might not work.
Download and install the latest version of Sideloadly on your computer. Ensure you have the web-version of iTunes installed (not the Microsoft Store version) if you are using Windows, as it provides necessary connection drivers. Step 3: Connect Your iOS Device facebook old version ipa
and community forums often host these files for preservation and testing: Internet Archive (Archive.org) This is the "million-dollar question
Tools like or Sideloadly let you safely install custom IPA files without jailbreaking. Step-by-Step Instructions: Step 3: Connect Your iOS Device and community
Is using an old version IPA legal? Generally, for personal use. You are not pirating a paid app—Facebook is free. However, you are violating Facebook’s Terms of Service (ToS). Section 3.2 of Facebook's ToS requires you to use the "latest version" of the software. If they detect an old client, they reserve the right to suspend your account. While rare for browsing, it is a risk.