I have an iPhone 6 Plus but can’t get iOS 14 but my friend with a 6 can I don’t understand

An iPhone 6 Plus is not capable of using iOS 14.

iOS 14 and iPadOS are compatible with these devices - Apple Support lists the 6s/6s Plus as supported.

• iPhone 6s and iPhone 6s Plus

You friend probably has a 6s, or 6s Plus.

The iPhone 6 and iPhone 6+ cannot be updated beyond iOS 12.4.8.

The iPhone 6S, however, can.

The iPhone 6 can not be updated further.

If your friend has a version higher than 12.4.8, they do not have an iPhone 6.