Hi there,
In this case, I don’t think there’s a way to show the mobile menu directly without a toggle, since the mobile menu can only been seen in the mobile header.
I would suggest using the same set of the primary menu on mobile, then add CSS to hide some of the menu items.
And go to Customizing > Layout > Primary Navigation, set the Mobile Menu Breakpoint to 0, so the menu won’t become toggle when the screen shrinks.
Hope this is helpful 🙂
Let me know if you need further assistance.