I set my new phone up using the backup, and I always worry about some weird issue arising if I load a previous iOS version backup on a new iOS device
I have had that happen in previous years. Only the problem was the other direction. When I updated my old phone to the freshly released iOS version it was actually ahead of the version that shipped on my new phone. I had to make a backup to iTunes, then when I ”restored” that backup to the new phone, I was prompted to install the latest iOS version first, which I did and it worked after that. But I couldn’t use the “transfer from old phone to new phone” option.
So now I will wait until I get the new phone, which will be iOS 18, and my old phone should transfer fine with an older version. At least that’s what I’ve been doing for the last couple of upgrades. They could have worked out that bug by now. I read somewhere that they can update an entire pallet load of new phone all at once with a new tool they have. So maybe that wouldn’t happen.