The iPhone upgrade program doesn't come with Applecare+ - the cost of the upgrade program is the cost of the iPhone plus the cost of Applecare+ divided by 24. If you complete the 24 payments the phone is yours free and clear - or you can after 12 payments opt for an upgrade to another iPhone.
You do get an interest free loan, and if you buy with Apple Card you do get a 3% rebate in your Apple Cash card.
Trouble is, iPhone resale prices being what they are, the iPhone you turn in is likely worth more than 50% of it's original price, so you'd be better off selling the old phone and buying a new one.
My current strategy (which was wrecked by my wife wanting my 11 Pro Max) is to buy the phone outright. I'm probably keeping my 12 Pro Max as a backup and to fly my Air 2, and dump my old backups: an iPhone 6 (which doesn't support a current iOS) and a iPhone 7 Plus (which my daughter used and cracked a corner of the screen and killed the battery on. It's not worth fixing the screen or getting a new battery for since it'll probably be subsetted soon).
Next year I'll probably buy outright again and sell the 13 Pro Max now that I have a serviceable backup.