WhatsApp usually stops supporting some versions of Android and iOS, to allow the company to introduce features that would not be possible on older operating systems.
In this case, WhatsApp will no longer be compatible with iOS 10, iOS 11 and therefore, with the iPhone 5 and earlier models in the coming months.
Apparently, WhatsApp will stop supporting iOS 10 and iOS 11 after October 24, 2022.
This means that if you are using iOS 10 or iOS 11, you will need to update to iOS 12 to continue using WhatsApp. Now this also implies that WhatsApp will no longer be compatible with the iPhone 5 as iOS 12 is not available for this model.
As we mentioned, removing support for certain iOS versions is necessary to support new features.