Electrum doesn't allow changing font size, unless you modify the code (font_size=X sp). Electrum follows the system's font DPI so you'll be able to change it by changing your Mac's font size in the system.
@ranochigo
I tried some typical ways and changed my system font size. While some texts on Electrum became larger in size (like texts on menu bar and buttons), codes written in console are still very small. Can you tell me how I can access (font_size=X sp)?