How to transfer traffic from an old domain to a new one with minimal losses?

Question

Domain name market

There is a site 6 years ago with a lot of visitors who come mostly organically to XYXYXY.wordpress.com, they leave various kinds of comments there, in general, the content still suits them. There is already a new domain XYXYXY.com and a ready-made new site on it. Part of the publications was moved, but somewhere in the last 15%. What are the general options for transferring traffic? I assume that a simple redirect from the old site to the main page of the new one can solve most of the issues. But again, I would like to somehow prepare users for the fact that we are closing the old site and transferring you to a new one.
If anyone has experienced similar situations, please share your experience.