The toggle menu (hamburger menu icon) to appear AND function on a wider screen (

The default setting where the toggle menu appears is the width of 860 px – I’d like to raise this to a width of 1108 px because this is the size where the left sidebar disappears.
My problem is that there’s a “dead space” between 860 and 1108 py when there’s no possibility for navigation…. only beneath the contents.
Of course I wouldn’t like a menu in the header – that’s why I’m looking for a solution.
A remark: even if I don’t have a menu (I do not visualize the menu), the toggle menu appears in the mentioned width. I was trying to visualize the hamburger menu icon (@media….) but it doesn’t open so I guess the setting should be done in function.js. I also had I try with that but since I’m not a JavaScript ninja ?? I didn’t manage to make it.
I would be grateful for any kind of solution.

https://postimg.org/image/vvdv0w5ip/