4:5 is the tallest ratio the Instagram feed shows without cropping, so it is the safest single export for a normal post.
9:16 is Reels and Stories. Labels are automatically lifted clear of the top and bottom of the frame here, because the reply bar and caption sit over roughly the bottom seventh of a Story. On a Reel the like and share icons also run up the right edge, so keep a bottom-right badge short or move it to the left.
1:1 is the ratio for carousels, since every slide is forced to the ratio of the first one.
3:4 is the classic print shape and reads well on Facebook and on a YouTube community post.
GIF is capped at 256 colours, so skies band. Keep GIFs short, keep the width at 480 or below, and use MP4 anywhere that accepts video.