Users of Whatsapp who use the app on iPhone 4 or the devices they still work with Android 4.0.3 (2011) can no longer use the app from 1 January 2021. iPhone models from 4S onwards can be updated to keep WhatsApp working, but older ones cannotsuch as devices that have the latest version of the Android operating system released in 2011.
It is a rather usual operation to discontinue support for older operating systems by WhatsApp. A standard practice for many technology companies, which cannot continue to support older and less popular hardware indefinitely. In any case, the number of users involved, the company says, is very low.