Sharepoint Online - Duplicate Site

Hello,

I'm the admin of Office365 for my company including Exchange, Teams and SharePoint Online.

I need to duplicate a customized SharePoint Online site (create a new one, keeping all designs and contents).

The size of the site is 18GB.

I've contacted Microsoft 1st support but they ask me to contact you directly.

Is there any script (PS ?) developed in order to do the action ?

Feel free to tell me any tips or ways to achieve.

Thx,

Pierre-François