Issue with Mobile-Style Menu on Desktop

Site URL: https://lebendige-gaerten.squarespace.com/

Hello, I could use your help. I’ve set up a mobile-style menu for the desktop version of my website, and overall it works well. However, on some computers (not all), there’s an issue: a thin white bar appears on the right side of the screen (see attached image). When you click on a submenu/dropdown, the white bar shifts left across the screen. Once the submenu is displayed, the white bar reappears on the right. The same thing happens when switching back from the submenu to the main menu.

How can I get rid of this white bar? It only appears on certain computers, regardless of screen size or browser. I’d appreciate your feedback!

https://www.lebendige-gaerten-hh.de/
pword: lebendigegaertenhh2023

You can use this to Website Tools > Custom CSS

div.header-menu-nav-folder {
    overflow: hidden;
}