If you still wish to attempt an installation for archival purposes or on a rooted device with compatibility layers, you must use third-party repositories. These versions are no longer updated with security patches. About supported devices | WhatsApp Help Center
Do not trust sites promising a compatible modern APK. The only secure way to use WhatsApp is to upgrade your hardware to a device running Android 5.0 or higher. whatsapp apk android 4.4 2 latest version