Wayne E. yeah you'll want to use a PAGE interaction called "page scrolled" and there are two triggers - "When scrolling up" and "When scrolling down". I would think that you'd have the navbar set to fixed like you have it and then adjust the position of the navbar if you wanted something similar to say the native mobile chrome/safari tab bars. You would use transform move with a negative top position equal to the height of the navbar - usually something like 5.5rem.
If you need a more solid example, I can whip one up for you - just let me know.