Linking a project to a repository works only in one direction

I created a repository and a project. Then I linked the repository to the project as described here:

Linking a repository to a project board

While I can access the repository from the project, access issues and move those to columns, close the corresponding issues etc, when choosing the projects tab in the repository bar (other tabs are Code, Issues, Pull requests, Actions etc), I can create a new project, how ever the existing one is not linked here.

How can I link my existing project such that it appears here?