This situation is tricky because iPad 2 is stuck on iOS 9.3.5, and WhatsApp no longer supports that OS. This content explains why it fails, what "portable" means, and the 3 real working solutions.
Pro Tip: Tap the Share button and select "Add to Home Screen" to create a dedicated icon for quick access. Alternative Solutions whatsapp for ipad 2 ios 935 portable
Furthermore, WhatsApp never released an official "iPad app." While you can use WhatsApp on an iPad via the web browser (Safari), that method requires a modern browser engine that iOS 9.3.5 can no longer support efficiently. This situation is tricky because iPad 2 is stuck on iOS 9
Getting WhatsApp to run on an older device like an iPad 2 (iOS 9.3.5) what "portable" means