WhatsApp has dropped support for iOS 9 with its latest update. This means if you use a very old iPhone that’s still running iOS 9, you will no longer be able to update to WhatsApp’s latest release.
The minimum requirement to use WhatsApp now is an iPhone that’s running iOS 10, which Apple first released in 2016. WhatsApp dropping support for such an old version of iOS should not really affect most users. As per the numbers released by Apple late last year, 81% of iOS devices out there are already running iOS 14, with 17% on iOS 13. The remaining 2% of iPhones are on iOS 12 or an older version of the OS, which is a very small number to bother anyone.
— WABetaInfo (@WABetaInfo) March 15, 2021
WhatsApp dropping support for iOS 9 is going to affect iPhone 4s owners the most. Considering the iPhone 4s was first launched in 2011, I doubt there will be many people out there in the wild who are still using the device as their daily driver. While the iPhone 5 is also no longer supported by Apple, it last received the iOS 10.3.4 update.
Do note that if you are using WhatsApp on an unsupported device, the app will stop working after a month or so from now. So, it is strongly recommended that you back up your chat and upgrade to a new device or export all your important chats so that you still have access to them.