Today my new iPhone arrived. Upgrade time!
First failure - don't back up to iCloud, it'll take forever. Back up to your Mac. Remember what Mac it is you back up to. And enable backup encryption. Because if you don't, it'll forget all your health data and all your passwords, and apparently also apps that require encryption. News to me.
Before this, though, unpair the Apple Watch from the phone. Because, it turns out that this is the only way to back it up.
So by unpairing (it takes about 5 minutes) you get a backup on your phone. Then you can backup your phone to a Mac, remembering to have it an encrypted backup, and THEN you can restore your old phone on the new, and only have half the apps be gone for no good reason.
Now you're just a confused panda, compared to the sad panda you'd be if you did it any other way.
Did I mention that the process around switching iPhones really needs improving? Apple engineers, I would expect you guys are doing this three times a day. Why is this not worked through? Let me just set up the new phone with a nod to the old phone, have all my info moved over securely, including the Apple Watch pairing and pairing with all other devices, and then have the old phone know it is now only a backup until at some point it is cleared out?