As of 2025, WhatsApp requires iOS 12 or newer . Your iPhone 4s is stuck on iOS 9.3.6, which is too old. WhatsApp no longer supports iOS 9 or 10.
Here's the direct, helpful answer you need: whatsapp iphone 4s ios 9.3 6 download
You cannot download or use the current version of WhatsApp on an iPhone 4s. As of 2025, WhatsApp requires iOS 12 or newer