There is no way to make a popup submenu or panel in MIDI Designer... yet!
Yes. You can make a button that jumps to a page.We're very well indexed by Google. "Jump to Page MIDI Designer" will get you there. If you include the word "manual" in your query, it will bring you here:https://mididesigner.com/wiki/doku.php/manual:chapter-working-with-layouts-banks-and-pagesThat's the User Manual.