Create submenu does not work with admin panel theme twenty

i want to create a submenu in the theme twenty like shown in the picture.

the structure looks like parent is "Schwerpunkte", which should not be routable (advanced settings routable disabled). child pages "chronische Erkrankungen", "Gesundheitscoaching" and "Hauterkrankungen" are Child pages. they are routable and visible. the submenu is not visible. Only "Schwerpunkte" without the subpages in the menu bar. I want it to like like shown in the picture
"Submenu".
What can i do?
thanks.

@seeankemone, Theme Twenty is not designed to fascilitate a menu structure as shown above.

It only provides a hardcoded menu-item 'Welcome' and a single dropdown menu 'Layout'. See the skeleton or the original theme.

You will have to change template /user/themes/twenty/templates/partials/header.html.twig to create a menu to you liking.

Note, this theme is 7 years old which is from the very early days of Grav. You might consider choosing a more recent theme.