Issue

Currently, the default breakpoint for the mobile menu is under 600px. This means that desktop header navs with long menus generally wrap in a very unattractive way before the breakpoint kicks with a hamburger button. See exaggerated example:

This is one thing I almost always end up overriding with the CSS customizer.

Suggestion

It would be great to allow the user to add their own breakpoint for the mobile menu. I think it would make sense to add this to the Navigation block, under the Display section, if the "Mobile" option is chosen. Quick mockup below.