Much has been said about this situation, however, for sure what will happen is that the operating systems that are installed on these computers will not be able to create new accounts or verify existing ones.
With these changes, it is planned that these cell phones will not support calls or messages from that app, that is, the messenger will stop working.
https://media.tenor.com/videos/1872d5a07fc75ee839d94661c38fa46a/mp4
All Android phones with operating system 4.0.3 or later will have WhatsApp after this date. However, all of the above will not support the application.
In the case of iPhone, all iOS 9 or later will continue to have WhatsApp, the rest are left out in addition to this some models with KaiOS will also support it although the Windows operating system computers will run out of WhatsApp permanently.
The recommendation is that if you really want to continue having WhatsApp, look for a more current model and that in general, it will offer you better performance of this and other applications.