Don’t be so quick to crop…
When you upload a 9×16 image or video when creating an ad, Meta asks you to crop or upload new creative that are square and wide for specific groups of placements.
Before you do that, preview your ads first. You may see that your creative in some of the placements that would have been square are actually 4×5. This takes up more real estate, which could make your ads more effective.
Facebook and Instagram mobile feeds, Instagram profile feed, and Video feeds could all benefit from the 4×5 aspect ratio.
If you upload a 9×16 video, it may appear as 4×5 in the feed. When you click it, it will open (nearly) full-length. That wouldn’t happen if you crop it or upload a square version. It would have displayed that sad, smaller version.
Another A placement is a location where your ad is shown. Examples include Facebook's mobile Feed, Messenger, Instagram feed, Audience Network, right-hand column, and more. More to watch is right-hand column. Meta requests 16:9, but it might actually look better square.
In all cases, preview by placement first. Depending on your creative, using the original versions may be preferred. Or at the very least, consider uploading 4×5 versions for the mobile feed placements.