If the main menu contains submenus, it's completely non-functional on mobile.
I thought it's a bug with my website, then a problem on mobile, but this is how youjoomla.com works with chrome devtools in responsive mode. the submenus are completely mangled.
Are you sure your are posting in product assigned forum?
What is your CMS version?
: Joomla 3.x
Link to installation
Have you edited any files? If yes tell us which ones.
Is this personal or client website?