While you can no longer find WhatsApp for Android 4.1.1 on the Google Play Store
Some versions of the old APK require Play Services for backup. Fix: Download a microG APK (open-source reimplementation of Play Services) and install it alongside WhatsApp.
Yes. Devices like the Samsung Galaxy S2 can run LineageOS 14.1 (Android 7.1) . This completely replaces Android 4.1.1 and lets you install the latest WhatsApp. This requires rooting and technical skill.
The APK is corrupted or requires a higher API level. Fix: Download WhatsApp 2.12.367 or earlier (these are much older but can be installed sequentially).
: You can find older versions on repositories like APKMirror or Uptodown .