EDGE-00-000006 - Background processing must be disabled.
Background processing allows Microsoft Edge processes to start at OS sign-in and keep running after the last browser window is closed. In this scenario, background apps and the current browsing session remain active, including any session cookies. An open background process displays an icon in the system tray, and can be closed from there. If this policy is enabled, background mode is turned on. If this policy is disabled, background mode is turned off. If this policy is not configured, background mode is initially turned off, and the user can configure its behavior in edge://settings/system.
Set the policy value for 'Computer Configuration/Administrative Templates/Microsoft Edge/Continue running background apps after Microsoft Edge closes' to 'Disabled'.