How to upgrade to ISO’s 14.0
How can I upgrade ISO’s 14.0
iPhone 6 Plus, iOS 12
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An iPhone 6 Plus can't be upgraded past IOS 12.5.6.
See the article(s) below which show device compatibility for each IOS version.
IOS 15 and iPadOS 15 Compatible Devices. *
iOS 14 and iPadOS 14 Compatible Devices. *
iOS 13 and iPadOS are compatible with these devices - Apple Support. *