When printing a layout in ArcGIS Pro, sometimes the sizes of the symbols appear differently in the printed output compared to the size displayed on the screen. This behavior is due to the variations in screen resolution and printer settings. For example, when the layout is zoomed in, the screen resolution may be high, which causes the symbols to appear larger compared to the printout. Furthermore, the printer settings may be set to a different paper size, causing the disparity in symbol sizes. If the paper size is smaller, the output symbols appear smaller as well.
As a workaround, manually set the symbol to the desired size before printing.