This is for Odoo 16.

First, select the page you wish to edit. 

Then, click on "Site" > "Properties (under This page)" > "Duplicate Page"

Name the new page, and there you go! When done with the duplication make sure to publish the page.

There is configuration-pages ( in the backend ) a duplicate options after selecting the page!
But not so sure if is not going to affect anything in the future ( settings related to the page)

My workaround:
After finishing the template page , with al the animations.. images.. colors.. etc, i took block by block and saved it, counted and rename theme 1, 2, 3.. etc
and upon creation of a new page, i just inserted them in the same order!
hope that helps