A portrait crop can suit a person, a tall product, a doorway, or a scene that has a clear vertical structure. It gives you more room above and below the subject than a square, but it still removes content from a source with a different shape. Start by deciding what the post needs to show, rather than selecting a format just because it is available.
This page exports our 1080×1350 pixel portrait JPEG. It is a prepared 4:5 file, not a guarantee of a particular display size in every Facebook feed or preview. For a person's portrait, leave space for hair, shoulders, and hands where they matter. For a product, check that the base and top remain inside the frame.
A landscape group photograph usually needs a different decision. Cropping it to portrait can remove people or make the remaining composition misleading. Use the album compressor to preserve the original proportions, or prepare a separate intentional portrait from a suitable source. The tool cannot extend scenery, move people closer together, or add missing background around an awkward crop.