I go from obsession to obsession. At the moment, it’s learning this program, but at one time, I was obsessed with repeating (tileable) patterns, understanding and creating them. Here’s a download link to two of them, originally used with solar plates to impart textures onto clay. No, they’re not square, but “Fern” is actually a square repeat, and close study will help you determine where to trim it for use. “Gator”, originally a pen and ink, can be easily deformed or altered to fill a square yet remain tileable. I used it to make an alligator shoe for Van Aken Clay, but I’m certain it has potential in ZBrush.
I thought folks mind find these useful.