There are several variations of square shapes (with scallops, angled corners, rounded corners, irregular) and while researching the question of square vs diamond shape from another forum I noted that the variations of square aren't always assigned consistently.
At the top of the shape selection in the filters are four general categories (any round, any polynomial, any with a hole, any scalloped).
I think that squarish coins are fairly common and a top entry of “Any square” would make it faster to filter in that case and side-step the question of what minor deviation on the corner changes a coin from square to square with angled/rounded corners.

