Two Facebook jobs, one ZIP of stills
Organic multi-photo posts
In a Page or profile composer, attaching several images often displays as a swipe. Square 1:1 (1080×1080 CSS, ~2160 exported) is the least surprising on phones. 16:9 works when every frame is cinematic and you accept more desktop-like framing. Export the ZIP, unzip, attach in order. Facebook will recompress. Keep subjects off the extreme edge; mobile UI chrome varies. This is not a cover-photo workflow — covers are a different crop (see the collage Facebook spoke if you are making a single banner).
Ads Manager cards
A Facebook/Instagram Advantage+ or carousel ad lets each card have its own link, headline, and description. Those fields are not in Collage/Carousel Studio. Design 1:1 product stills here (catalog-friendly), download, then upload into the ad or into a catalog that the ad reads. Dynamic product ads that pull from a feed do not need this studio at all unless you are manufacturing the image files the feed points at.
Shop and catalog honesty
A “Facebook product carousel” in ads-speak is usually a catalog. We will not pretend the Save All button pushes SKUs to Commerce Manager. If you need lifestyle + pack-shot + scale in one organic post, a three-frame ZIP is the honest asset. If you need ten SKUs each with a shop URL, you are in catalog land. Mixing those stories in one paragraph is how stuffed pages happen; this one stays on files.