The solution to that is to make your menu items stack like in the screencast below.
To achieve that, set the Navigation Inline > Self Flex to Standard and enable Wrap Children under Flex Layout. For more details about the option, please see the Navigation Inline's documentation at https://theme.co/apex/forum/t/elements-navigation-inline/14639
Having an understanding of Flexbox will also be helpful. Please see our Flexbox tutorial at https://theme.co/apex/forum/t/using-flexbox/24851
You can also hide the Navigation Inline element and show a Navigation Collapsed element in its place. That's made possible by the elements' Hide During Breakpoints option.
In that setup, you'll have the Navigation Inline showing desktop and Navigation Collapsed showing in mobile view.
Hope that helps.