NO UPDATE TO iOS would be complete without new features for Safari, and this one definitely delivers. The way Private Browsing works has been overhauled, giving you more protection when using a private tab.
If you leave a Private Browsing tab open and your phone locks, then the private tab also locks. When you unlock your phone again, you have to unlock your Private Browsing tab separately with Face ID, Touch ID or your passcode. This new feature is useful if you forget you had the private tab open and hand your phonelooking at, which is what private browsing is all about.