what counts as instagram post look?

Do you mean the size or the style? Size-wise, portrait 4:5 (1080 x 1350) takes up the most room in the feed, square 1080 x 1080 still works, and reels and stories are 9:16 vertical. The profile grid now shows a taller crop than the old squares, so keep text and faces away from the top and bottom edges or they get cut off on the grid. If you mean style, scroll the accounts in your niche that are doing well and you'll see the pattern quickly.