What levels of the ArcGIS Enterprise stack support (or don't support) scheduled jobs?
Types of GIS scheduled jobs:
What are our options? Is the above list correct?
I think your assessment is correct, ArcGIS Server and ArcGIS Portal do not have any built-in task scheduling functionality. My impression is that Esri's introduction of scheduled tasks with Notebook Server is their approach to introducing scheduling within the ArcGIS Enterprise platform.
Even though ArcGIS Server and ArcGIS Portal do not have built-in scheduling mechanisms, both products implement the ArcGIS REST API, and you can run scheduled tasks from other systems to call the REST API to automate work. In short, not having built-in scheduling doesn't mean it can't be scheduled.