There are a lot of different fonts you can use in your bullet journal. It can be fun to experiment with new fonts, or to use different fonts for different purposes. You might want to use a more elaborate font for headings, and a simpler font for the body of your journal. You could also use different fonts for your monthly and weekly spreads.
Some people recommend using a simple sans-serif font for your bullet journal, because it's easy to read and write in. Some popular sans-serif fonts include Arial, Calibri, and Helvetica. If you're looking for something a little more decorative, you could try using a script font or a calligraphy font. However, be aware that these fonts can be tricky to write in, so you may need to practice a bit before using them in your journal.