They are replaceable. I've replaced batteries in older iPhones plenty of times, had Apple replace the battery in a few, and I'm probably going to use the Self Service program to get the parts for my 14 Pro Max soon as it's getting a bit tired out.
I suppose that anything is "replaceable" if you're willing to involve things like soldering irons, heat guns, or specialized tools, but replacing a battery on an iphone is not something that the vast majority of the population would be equipped to do or be comfortable doing.
