I have not witnessed a PSM-I training where the class did not add "Stakeholders" to their drawing of the Scrum framework. There are different kinds of Stakeholders (the business, customers, users,...), but with Stakeholders students usually mean "the business people trying to influence product development through the Product Owner". To add these Stakeholders to the Scrum equation makes total sense considering the Stakeholders' powerful impact on the product. Stakeholders are related to the family of roles, but they are not a Scrum role. This is because (business) Stakeholders do not actively contribute in the creation process of the increment during the Sprint. When the Stakeholders are invited by the Product Owner to the Sprint Review, they contribute by inspecting the increment so they can provide feedback on product value. The Stakeholders play an important role in the background with the Product Owner acting as a lens towards the Development team.
The Sprint goal is not an artifact but an objective set for the Sprint. The Sprint Goal is crafted by the Scrum team during Sprint Planning and guides the Development team to why it is building the Increment while offering them solution flexibility. The Sprint Goal is not an artefact as it is not inspected or adapted, i.e. it is not used to do empirical process control. It is crafted and then used as a guide for the inspection/adaptation throughout the Sprint.