If you are using an old Android phone then it is better to replace it, otherwise it will not be possible to use WhatsApp.
Yes indeed, WhatsApp is ending support for many older Android phones in late October.
After October 24, WhatsApp will be available only on phones running Android 5.0 or later operating versions.
This announcement of WhatsApp FAQ page I have been
According to the company, WhatsApp can currently be used on Android 4.1 or later operating systems, but from October 24, 2023, support for the messaging app will be provided only on Android 5.0 or later versions.
That means WhatsApp support will be removed for all operating systems prior to Android 4.1 or Android 5.0.
WhatsApp said in its FAQ page that when support for an operating system ends, users are notified ahead of time and advised to upgrade.
Note that WhatsApp is constantly improving the user interface and privacy settings, introducing features that are compatible with the latest Apple and Android operating systems.
For those using WhatsApp on iPhone, devices require iOS 12 or later.
Well, most of the Android phones still have Android 5.0 or later versions, but there are also quite a few older phones that are using older operating systems.
Note that earlier WhatsApp ended WhatsApp support for iPhones running on iOS 10 and 11 on October 24, 2022.