As a user, I would like the + Create Issue in Epic button to open a pop-up that allows me to change the project of the issue I am creating in the Epic as it happened in the old issue view.
The in-line creation only allows you to create issues in the Epic that belong to the same project.
Open a pop-up window to allow me to select issues from other projects.
Set a field as required in the projects to enforce the pop-up screen to fill the required fields.
Edit: Workaround does not work anymore because of the bug JRACLOUD-75648.