Is it safe to update iPhone 14 plus to iOS 18

99.99% safe. But with many millions of users updating, a few things are bound to go wrong.

In fact, if millions of users did nothing except power off and restart their phone, a tiny fraction of users would have problems.

If you are looking at other posts on this site, notice that everyone here has a problem. It's like a hospital. No one ever posts to say that the update is working just fine......except me, maybe.

Users who do not have problems are not usually even coming to this site.