In Processing Java, when you export a project, you get this screen:
In p5.js mode, currently you don't have an option to turn on presentation mode by default in your exported application. My use case for this is to be able to bundle a p5 sketch into a nice single application that can be given to gallery technicians responsible for keeping it running -- the fewer steps I can give them, the better, so it'd be great to have the application immediately jump into fullscreen. Not sure any of the other settings apply, but having a window with at least the presentation mode toggle would be great!