You can flash a Custom ROM (e.g., LineageOS) onto your device to upgrade it to Android 5.0+ or higher, though this requires technical knowledge.
WhatsApp for Android KitKat 4.4.2: How to Download and Use Old Versions Whatsapp For Kitkat 4.4 2 Download Old Version
Do not download APKs from random, unverified websites, as they often contain malware. Use trusted, historical app repositories: (Highly Recommended) APKPure Uptodown Step 2: Choose the Correct WhatsApp Version You can flash a Custom ROM (e
Step-by-Step Guide to Download and Install WhatsApp APK on KitKat Whatsapp For Kitkat 4.4 2 Download Old Version
Before proceeding, understand that you are installing an app outside the Google Play Store. You must enable "Unknown Sources" and accept that this version is no longer receiving security updates.