We have a general project with Epics which all or some teams have to work on. By selecting a custom field value the Epic shows up on the Agile board for the related team(s). Then the team can associate the issues from their own development project with the (general) Epic.
In plans however I only see the Epic and not all issues associated with it as these are in different projects.
What general filter can I use to select the "Epic Project" and the issues linked to the Epics in that project so they show up in the Plan.