Should I do an automatic redirect from the old site to the new one?

Question

Google

Hey!
A couple of years ago I made a website for selling services, about a year later I decided to change the domain and cms. As a result, I made a new site, and left the old one (to the content, the new site is practically a copy of the old one).
Now about 20% of requests from the search come from the old one and it directly competes with the main site (plus, apparently due to the fact that the content of the same new site goes down in search results).
Tell me what to do with the old site? Make an automatic redirect to a new one or leave it and let it work for itself?

Answer 1

Make a redirect.
The weight of the old site will be added to the new one.

Answer 2

Do 301 redirects page by page from all pages of the old site to the pages of the new site.

Answer 3

Make page-to-page redirects based on changed URLs