WhatsApp has dropped support for an older version of Android, dropping support for Android 4.4, otherwise known as KitKat.
WhatsApp routinely drops support for older versions of Android when their usage numbers drop low enough or it becomes too difficult to support those versions securely.
Spotted by Android Police, WhatsApp has now officially dropped KitKat support. Fortunately, only 0.5% of users still rely on the old version of Android.