The steps above allow you to change the font of selected parts of your notes, but new notes will revert back to the original default size. Change the Default Font Size in Notes for macOS In addition to using the Fonts window, you can use standard formatting keyboard shortcuts to modify your Notes text, such as Command-B for bold, Command-I for italics, or Command-= to increase size. This will open the default macOS font window, where you can choose to format your selected text with any installed font at any size.
With your text selected, go to Format > Font > Show Fonts from the menu bar, or use the keyboard shortcut Command-T. Next, use your mouse or trackpad cursor to select some subset of your note, such as a word or sentence. To try it out, open an existing note or create a new note and type some text. Unlike older versions of the Notes app, which used a single font for all notes, the more advanced version of Notes found in macOS Sierra lets you change the font of individual words or lines within a note, just like you can with a word processor like Pages.
Change Font and Size for Selected Text in Notes for macOS
