custom CSS to hide header

Just the menu? Add this to the Additional CSS panel of the customizer:

.page-id-14 .navbar-header {
    display: none;
}

This only hides on page ID 14. To hide on other specific pages, add similar selectors, separated by commas. For example:
.page-id-14 .navbar-header, .page-id-22 .navbar-header, .page-id-66 .navbar-header

Hi, thanks for the answer.
Unfortunately this is not working.
The menu does not disappear.

My bad, I had a smallish window open, which triggered the mobile menu. The previously provided code only hid the mobile hamburger menu. Try this instead:

.page-id-14 .navi {
    display: none;
}

Should hide both kinds of menus on page ID 14.

Thanks again. I seem to be having an issue with the custom CSS, it does not seem to work. I have deactivated all plugins, but no change.
No idea what the issue could be?

it seems to work for the page you posted, i.e. the front page.
any other specific pages will have different .page-id-??? numbers.
or could be caused by your used cache…

You were right, when I cleared the cache, it worked for the front page.
it is actually for a post and here it does not work.

https://www.dr-scheib.de/psychosomatische-grundversorgung-kompaktkurs/

I have used this:

.page-id-820 .navi {
display: none;
}

and also tried:

.post-id-820 .navi {
display: none;
}

Thank you very much!

Check the body tag for correct class for post IDs. It’s .postid-820 .navi selector (only one hyphen)

Thank you so much, that worked!!!