Can iPhone XR update to iOS 18?

The iPhone XR is compatible with iOS 18.

If the phone is on some version of iOS 16 right now, it will probably be offering you updates both to iOS 17.7 and to iOS 18. I updated my phone from iOS 16 to iOS 17 just the other day – so I doubt if being on iOS 16 is keeping you from doing an update.

If you are running a beta version of iOS 18 on your iPhone 11 Pro Max, that might interfere with features like Quick Start, or with restoration of a backup to a new iPhone. It's a good idea to run beta versions only on spare phones that you do not need for everyday use – not on phones that you must rely on every day.

Another question. Did your friend prepare the phone properly for transfer?

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

If he did, the phone should have opened up to the "Hello" screen. If it didn't, take it back to him. Ask him to carry out these steps and then return the phone to you.

As for using iMessages, you should be able to do that on iOS 16. Maybe if you describe the problem you are having with that in more detail, someone could suggest a fix. Then you could make the decision on what iOS update to install (if any) on its own merits.

If you can’t turn on or sign in to iMessage or FaceTime on your iPhone - Apple Support

If you are on iOS 16 now, and you have automatic updates disabled, your choices are as follows:

1. Remain on iOS 16.
2. Update to iOS 17.7. (Limited-time choice; may disappear without warning.)
3. Update to iOS 18.

I can see why you might be cautious. Your phone has only 3 GB of RAM – it is one of only two models compatible with iOS 18 to have that little. It also is one of the oldest iPhones that can run iOS 18.

My iPhone is somewhat newer, with a bit more RAM – but I decided to go with door 2, while I still could. Choosing door 2 does not keep you from choosing door 3 later. Once you choose door 3, you can never go back …