By default, header element “Main menu” is show menu that is selected as main menu in menu editor (https://prnt.sc/1v9lon0). For now you set your categories’ “Bal oldali menü” menu as main menu, and it was displayed in header main menu element. To fix this issue:
1. Try to assign other menu as your desired Main menu in WordPress menu editor.
2. Navigate to the Theme Settings => Shop => Sticky categories navigation and set your categories’ “Bal oldali menü” menu as your sidebar sticky menu.