Deactivate drop down arrow of main menu

alphabar

Hi team, I want to deactivate the possibility of dropping down the main menu.
I'm talking about the arrow that is on the right hand side and pulls down the menu and opens up more menu space.

Where can I deactivate that arrow?
Appreciate your help!

Air

Hello

Please show on screen shot what you mean cause I am a bit confused:-) Thanks!
With regards.