A Highlight cover has very little space to explain itself. A simple icon, a recognisable object, or a clear face can work better than a complete poster. Tiny words, multiple symbols, and busy backgrounds become difficult to distinguish when the cover is viewed beside other circles on a profile.
This page opens our 720×720 pixel square export. It is a source preparation choice, not an official Highlight-cover dimension claim. Instagram lets you choose the visible cover area in its own interface, so inspect that circle before saving. The corners of a square are not dependable places for an essential mark or letter.
Create the artwork in a design app first. The tool can crop, resize, sharpen edges, and encode a finished image; it cannot draw icons, add text, recolour a logo, or generate a matching set of covers. If you want several categories to look related, give their source designs consistent margins, stroke weight, and background treatment before export. Different shapes can appear different in size even when their source canvases have identical dimensions, so judge them visually rather than by numbers alone.