The story mapping app global configuration allows to enable the app only for certain projects. When the toggle is turned to "on" the app will be available for all Jira projects.
When turning this setting off, you can manually add projects to the list of "allowed" projects.
Please note that this feature is primarily used to control the project menu entry. It does not exclude issues from projects to be included in a portfolio map or board filter that is used within the portfolio map.