Nabeel Azam

you must be using a third party menu plugin,

If yes then try removing that plugin or disable the visibility of the mobile menu on the desktop screen from that plugin settings.

If not then you need to make sure that you are not using a child theme on your website.

If the issue still persists please elaborate this issue more

sorry, I cleared the cache of the browsers but not of the website. The problem is fixed and thanks for getting in touch.