Hi there,
you can build any kind of Post Meta with a GeneratePress Block Element and GenerateBlocks.
Our blocks support many dynamic data types including title, terms, dates ( published and latest ) as well as post meta, term meta and author meta etc.
I can recount a few support topics where we have shown users how to add a “co-author” or reviewed by author in their post meta. So that too is possible today.
However when it comes to co-authors, the question is are they:
a. a true co-author where a single post can be attributed and archived by multiple authors
OR
b. custom meta for displaying another author.
Option b can be done today. Option a is not a native WP function, and ideally it should be.
You can use plugins such as the one by publish press to handle that ( i think ) and they have an API that could be integrated with a GP Block element with very little code.
Linke to API for reference:
https://publishpress.com/knowledge-base/the-authors-api/