Apologies for the inconvenience.
Based on the symptoms you are describing, this is most likely related to a module assignment issue rather than a missing extension. Please check whether there is any module published in the menu position that does not belong to the current template or builder setup.
As a first step, I recommend temporarily unpublishing any custom or legacy menu modules that are assigned to the menu position and then clearing the cache. In many cases, a conflicting or outdated module can prevent the template CSS and menu structure from rendering correctly.
Once the conflicting module is disabled, the menus and overall layout should load as expected. If the issue persists after this, please let us know and we can review it further.