No, access must be configured for all microflows which are triggered by a client action. A button, widget event, navigation items.
Sub microflows inherit the access from parent.
Scheduled events are handled by the server, w/o a user account involved.
Event handlers inherit from entity access. I.e. when you are allowed to create an object, an after create can be triggered
Nanoflows must always have access configured, as the run in the client.
Access needs to be configured only for Main microflows. No need to configure microflow access for sub microflows. Sub microflow will get triggered based on parent microflows