Hello,
Thank you for the question.
Yes, we hide this mega navigation for mobile devices since it can’t fit the space well and may cause a lot of appearance problems. But a solution is very simple: you just need to add all categories you want to the side mobile navigation. Go to Appearance -> Menus -> create a new one and mark it to be “Mobile menu”. Then just add all the necessary pages and product categories there so your visitors may easily access them from their mobile devices.
Regards