Explanation

Box 1: Site Map validation
When you validate the app, the app designer canvas shows you details about the assets that are missing.
In the app designer, select Validate.
A notification bar appears and shows you whether the app has any errors or warnings. The notification bar shows warnings in cases where, for example, an entity has no forms or views, or the app doesn't contain any components. An error might appear if a site map isn't configured for the app.

Reference:
https://docs.microsoft.com/en-us/dynamics365/customerengagement/on-premises/customize/validate-app
https://community.dynamics.com/crm/b/crminthefield/posts/monitoring-the-power-platform-canvas-driven-apps-