For those who might be wondering, iOS 4.2.1 was a significant update back in 2010, bringing several enhancements and features to the iPhone, including AirPlay, iAd, and improvements to Mail and Safari. Fast forward to today, and while iOS 4.2.1 might seem like a relic of the past, there's still a community of users and developers interested in retro tech and app versions.
The subreddit r/LegacyJailbreak maintains a Google Drive archive of old IPAs. Search the subreddit for "Messenger iOS 4" or check their pinned "IPA Spreadsheet." You will frequently find direct download links for Facebook Messenger v4.0 and v4.1.1. facebook messenger ipa for ios 4.2.1 download
: Facebook Messenger no longer supports iOS 4.2.1. The last compatible version was released around 2012–2013, and Facebook has since shut down servers for many legacy APIs. Even if you install an old IPA, it likely won't connect to Facebook's current servers. For those who might be wondering, iOS 4