Menu Displayed Twice on Helix Ultimate

Hello,
I'm creating the template for this site (https://wjjc.eu/biz/) with Helix Ultimate and SP Page Builder Pro.
I created a custom header consisting of two rows and three columns that displays properly on desktop and shouldn't display on mobile. So far, so good.
In the template, below the header, I added a row with the menu position, and this also displays properly on the desktop version.
The problem arises when displaying the menu on the mobile version on off-canvas with a burger icon.
After countless attempts, I resorted to a default header, setting the desktop logo size to 0, but the menu appears duplicated at the top of the header.
Again, the problem is in desktop view, where the menu contained in the menu position displays twice.
It's likely that a CSS file that prevents the menu from displaying, or even better, the default header only on desktop, will resolve this, but I haven't been able to.
I would have liked to use just one section for this, but I couldn't. As far as the webmaster is concerned, it wouldn't be a problem, because that's me. :-) Can you help me with some CSS to fix the display issue?
I'm asking for your kind help.
Thank you