Facebook started testing a new set of image presentation options for posts last October, with defined display formats for multiple images uploads, allowing users with more ways to display visuals.
The format has been spotted by many users since then and it seems to be getting a wide release with various reports of the option showing in the composer for multi-image posts.
The new option is seen at the bottom of the post composer offering users four different display formats to select from. This indeed offers new considerations for your Facebook posts which possibly would help to make your updates stand out in feeds. From the perspective of a brand, these formats can be used to better display your products and enhance promotion with new added angles and display tools.
As of now, it seems to be available for personal profiles but it might be expanded to Pages too which offers a new option to consider. So, if you are not getting the option to use new display formats then they are likely to roll out to you anytime soon.