Working with a default configuration of the X theme set to the Integrity stack, I would like to add a second menu so that I can have one show up for mobile only but another one entirely show up for mobile screens. Ultimately I will be adding a menu to the top bar so links are split between desktop nav and top bar, but when the layout changes for mobile, I would like to specify a different menu entirely.
X theme does not have function however you could use a compatible plugin with X theme which is Superfly. You could use superfly to show different menu on mobile version. If in case you will not use superfly, regretfully saying that you would need a custom developer to creating a function like that.