In this panel, you will see a slider labeled . Dragging this slider to the left reduces the icon dimensions down to a tiny 16x16 pixels. For a truly minimized look, also adjust the Grid spacing to a tighter setting and set the Text size to its smallest legible value (e.g., 10 pt). Unlike Windows, macOS does not have a discrete "extra small" preset; the slider provides continuous control down to the pixel level.

Scroll the (towards you) to decrease the size of the icons.