square-medium from coolicons in Line with regular corners. box, rectangle, stop, checkbox, frame. Other styles and corners: @coolicons/<style>/<radius>/square-medium with line, duocolor, duotone, fill or bulk and sharp or round. Leave out regular, like @coolicons/fill/square-medium, and use @coolicons/square-medium for line with regular corners.
pnpm dlx shadcn@latest add "https://coolicons.cool/r/square-medium.json"