WhatsApp will soon drop support for another round of older versions of iOS and Android. As described in WhatsApp’s recently updated system requirements, you must have a device that runs at least iOS 9 or Android 4.0.3 in order to access WhatsApp after January 1, 2021.
source https://lifehacker.com/whatsapp-is-ditching-these-old-phones-in-2021-updated-1840367419