Is it possible to glue the domain mirror?

Question

Google

There are two domains. I want to make one domain a mirror of another domain.
But will the gluing work in Yandex and Google search engines if the page address is the same, but the pages will be 20% fewer and there will be a different design?
I seem to have read somewhere that you can glue mirrors if the sites have a different design. But I can be wrong.

Answer 1

canonical and forward

Answer 2

What does it mean if the page address is the same? Put a 301 redirect on the main mirror and that's it