Unfortunately it is not possible to get a notification immediately after any flow has failed. If you want to get notified, you have to catch error messages from each action in the flow.
Unless we use the Scope feature! All errors that occur within the scope can be cached with an action following on this scope. So for example:
The “Configure run after” state selection for the action “Send error message” is “has failed” and “has timed out”.
So when an error occurs within the Scope, the email is being send (or notification, if wanted). Unfortunately this cannot be handled within a Child flow due to technical reasons. At the end of the failed flow I added a “Terminate” control to finish the flow with the failed state.