My 6s does not update iCloud and software version from 13 to 14

Your profile states that you have an iPhone 6 Plus running iOS version 12. Your iPhone cannot be updated past iOS version 12.5.1

One thing that you should know and confirm and that is whether you have an iPhone 6s or do you have an iPhone 6 (Without the S) This is important because an iPhone 6 can only be updated up to iOS 12.5.1 and NOTHING HIGHER. You need an iPhone 6s to update higher than that to iOS 14.x. Double check which iPhone you have.

Open Settings ➔ General ➔ About ➔ Model Name: What does it state there?

Axel F.