While you can find legacy files for iOS 4.2.1 through community archives, they are non-functional for messaging today. WhatsApp has deprecated support for all versions below iOS 15.1 , and their servers will block any connection or verification attempts from these outdated versions.
Forums like Reddit's r/LegacyJailbreak often host links to archived IPA files for "golden age" iOS versions. Ios 4.2.1 Whatsapp Ipa Download
: To install a custom IPA on such an old firmware, the device typically requires a jailbreak and a utility like AppSync to bypass Apple's signature checks. Current Alternatives for Old Devices WhatsApp IPA While you can find legacy files for iOS 4