Multi-photo posts are supported
People can open and move through several photos, although Facebook may first present the post as a grid or collage.
FACEBOOK CAROUSEL ANSWER
Can you post a swipeable carousel on Facebook?
Facebook supports posts with multiple photos, but the grid or swipe experience can vary. An ordinary post cannot contain your own custom HTML carousel.
Custom HTML is not embedded
An interactive HTML carousel can be shared only as a website link; it does not become a native carousel inside the Facebook post.
Use a Reel for fixed order
A Reel is the predictable option when a tutorial, story, list, or set of memories must appear one image at a time.