Website is Not Responsive at Mobile

Hi, how are you?
I was working on a project based on your theme, however, it seems that the theme was not made to present the content in the mobile version.

The structures are all collapsed on mobile.

Can you tell me the reason for this error?

Tried viewing on an iphone 12 pro max, iphone 13, iphone 7 and in Chrome, Internet Explorer & Safari browsers.

The page I need help with: [log in to see the link]