Perfect thank you

theme option - header and menu - will give you many settings for menus (available also in customizer). Check also link which I sent if you need Mega menu

Is there any way to actually style the menu? For remove the lines for each
menu item like this - | MENU | or having a hover over color

Theme has own mega menu so you don't need any plugins http://rehubdocs.wpsoul.com/docs/rehub-theme/basic-settings/mega-menus/

It seems to be a problem related to using the Mega Max Plugin. is there any support for using this plugin ?

https://wordpress.org/plugins/megamenu/

Hello, when I test my site on mobile resolution the menu 3 bars display a blank nothing but a dark overlay. Where is this controlled from?