Why is this update important

Hi Jed34-,

Welcome to the Apple Community.

Wondering which update you mean ?

Seems iOS 12.5.4 is the latest update that can be installed on iPhone 6

iPhone 6 lacks the components to use iOS13, or any software higher.

Updating to the highest number iOS you can use is usually the safest option.

Apple support has an article online that could guide you:

Update iOS software on iPhone

https://support.apple.com/en-au/guide/iphone/iph3e504502/12.0/ios/12.0

Hope this helps you :)

Jed34- Said:

"Why is this update important"

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Find Out why here: About iOS 14 Updates - Apple Support. Read the top paragraph --from a general standpoint, it tells you what updates are important.