Menu with pages of Level 1 & Level 2 (selective)

Hello Currently I'm trying to get a handle on the menu, which unfortunately I can't.

I would like to create a menu structure, in the pages from level 1 of the pages this also works wonderfully.

I would like to create a menu structure that includes pages from level 1 and pages from level 2. However not all, but only selectively chosen pages. E.g. I would like to have topic_1, topic_2 and topic_3, beside about ... and the imprint in the menu.

So the menu should selectively consist of level 1 and level 2.

I have already inserted "onpage_menu: true", but without success.

How could I do something like this with the Antimatter Theme?

Thanks in advance.

The structure:

root
about_this_blog (default -> visible in MENU)
blog (NOT visible, ??? -> NOT visible in Menu)
    topic_1 (as a blog -> visible in MENU)
        item_page_01
        item_page_02
        item_page_03
        item_page_xx
    topic_2 (as a blog -> visible in MENU)
        item_page_01
        item_page_02
        item_page_03
        item_page_xx
    topic_3 (as a blog -> visible in MENU)
        item_page_01
        item_page_02
        item_page_03
        item_page_xx
imprint (default -> visible in MENU)
about_me (default -> visible in MENU)