It seems iPhone does not support WhatsApp?

iPhone 6s, iOS 11

WhatsApp requires iOS 12.0 or later.

You can update your iPhone 6S to iOS 15.7.2, but not to a higher iOS (16 and later).

For sure please check your iPhone model & iOS version -> Go to: Settings -> General -> About.

You can check by reading this Apple article: iPhone models compatible with iOS 15

iPhone models compatible with iOS 15.5 – Apple Support (UK)

Then go to Settings -> General -> Software Update -> Download and Install.

You need about 6 GB device storage and good Service & Wi-Fi.

If they are On, turn Off Hotspot & VPN.

Charge the battery > 70%.

See the following Apple articles:

Update your iPhone, iPad, or iPod touch

Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If your iPhone, iPad or iPod touch won’t update

If your iPhone, iPad, or iPod touch won't update - Apple Support

You can do the update via PC, see this Apple article: Update software on iPhone, iPad or iPod touch in iTunes on PC

Update software on iPhone, iPad or iPod touch in iTunes on PC – Apple Support (UK)

If you have a Mac see this Apple article: Update your iPhone, iPad, or iPod touch with the Finder

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

Akwaánàebelego wrote:

It seems iPhone does not support WhatsApp?

Then time for you to upgrade to a newer phone that is compatible with whatsapp.