I'm trying to assign this issue to this project, both created by myself within my organisation. In the "Projects" tab, on the issue's right column, I can't see the project. Before, I tried to add repositories, but I can't see them either.
Maybe I'm getting something wrong, my idea is that the 'Projects' bit is to say which component/project/tool the issue is about (at least, I'd like to use it this way).
Althought the project board you referenced is no longer active, I know the issue you're having and have a fix. If you want to reference an issue from one repository to a project board, you can copy the URL of the issue and paste it into a note that was created in a project board's column (creating a note can be achieved by clicking the + symbol in the right-hand corner of a project board column.) I hope this helps!