What format each post publishes as

In the composer, each network row shows a badge with the format that will actually be published: Text, Photo, Carousel, Gallery, Video, Reel, Story, Thread or Document.

Instagram decides the format from the media, not from a dropdown:

• 1 photo = a normal feed post.
• 2 to 10 files = a carousel. Photos and videos CAN be mixed in the same Instagram carousel.
• 1 single video and nothing else = a Reel.
• To publish a Story instead, choose "Story" in the Instagram post type option.

Facebook has a post type option with Feed, Reel and Story.

The composer also warns you when your images do not fit a network. Instagram feed and carousel images must have an aspect ratio between 0.8 (4:5 portrait) and 1.91 (landscape). A 9:16 vertical image has to be published as a Story, or cropped. Use the crop button on the image to fix it to 4:5, 1:1, 1.91:1 or 9:16.

In an Instagram carousel all items should share the same aspect ratio, because Instagram applies the ratio of the FIRST item to the whole carousel and crops the rest. Ignix warns you when the ratios do not match.