Why my iphone didnt update?

Julia_A Said:

"Why my iphone don't have any update?"

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Installing Post-iOS12 Updates:

This is not an option. Your iPhone model (6 Plus) is incompatible with iOS13 and/or iOS14  and/or iOS15. This is because your iPhone model (6)does not meet the hardware requirements for this iOS version(s). So, you cannot update the iOS.

So..

Install In-App Updates:

But, this may not restrict your form installing in-app updates. So, open the apps, seeing what you can install.

See why in this compatibility chart: