"Apps like Instagram have a standard carousel for photo albums"

Yeah, but that only applies to users who are used to Instagram. It's definitely not an INTUITIVE feature.

I've had friends and family link me to Instagram posts, and though I've learned now, for a long time they'd have to explicitly mention there were additional pictures in the post, or I'd miss them.

(I don't know if it's different in the app, but certainly in the webpage those little dots at the bottom are non-obvious to a first-time user.)