It sounds like you're interested in two distinct things: finding an older version of WhatsApp for a legacy device (Android 4.4.4 KitKat) and perhaps getting into the world of app development or feature creation. 1. Downloading WhatsApp for Android 4.4.4
Download the verified APK file directly to your phone or transfer it from a computer via USB. Open your device's app. Locate your Downloads folder. Tap the WhatsApp APK file and select Install . Alternatives to Using Outdated WhatsApp APKs
WhatsApp 4.4.4 APK Download: How to Install It on Older Android Devices
WhatsApp includes a hardcoded expiration date in its app code. Once that date passes, the app prompts you to update.
For tech-savvy users, flashing a Custom ROM (like LineageOS) can upgrade your device to a newer Android version (e.g., Android 7.0 or higher), allowing official WhatsApp support.