p5.js is easier to learn and more adaptable, processing is java so its waay faster and can be exported to an EXE (but not really a secure one you need external sources for that) . There are ways to make a JavaScript exe using https://electronjs.org/ and such but Its truly meant for web development and p5.ja just makes the visual waay easier, allowing you to do things without really having to edit css or html (but it is good to know how to) or any stuff like that. p5.js and processing have in-depth tutorials by Daniel Shiffman https://www.youtube.com/channel/UCvjgXvBlbQiydffZU7m1_aw