While it's possible to download and install WhatsApp on an iPhone 4s with iOS 9.3.6, there are limitations and considerations to keep in mind. If you're looking for a seamless messaging experience, you may want to consider upgrading to a newer device or using alternative messaging apps. However, if you're determined to use WhatsApp on your iPhone 4s, follow the steps outlined in this article to get started.
If WhatsApp stops working tomorrow, here are better-optimized alternatives for your iPhone 4S:
This is the only safe, official method. Apple and WhatsApp allow you to download the last compatible version of an app even if your iOS is outdated.
Only as a backup phone or for nostalgia. For daily messaging, the lack of call support and upcoming forced obsolescence make it unreliable.