What is the latest update for a iPhone 6

Do NOT update it - iOS 12.5 will kill your iPhone 6's battery in minutes. I went from 100% charged to 70% charged while it was "asleep" with no apps running in the background.

You can turn off Exposure Notifications in Settings, but it's still not ideal.

iOS 12.5.

For a 2nd or 3rd generation iPad mini, iOS 12.5 is the highest possible.