Menu mobile an tablet does not ork

I’m quite a newby and I have a problem with my website in combination with my mobile phone. The menu button on little screens doesn’t work. I don’t know what I’m doing wrong, but tried several times and several forums to resolve my problem.
I use the most recent theme version of the theme Gridiculous.
Maybe someone knows what the problem is… When I’m pressing the menu button on my mobile phone or desktop (in smaller size), i get in my URL a #.
I’m using an ‘under construction plugin’, so when someone needs me to deactivate the plugin, you just can say.
The website is: https://www.autorijschooldewind.nl
Everyone who reacts, thanks for trying….
(excus for my bad English, I’m from the Netherlands) ??