Plato's shadows have absolutely nothing to do with living in a simulation. He was talking about degrees of true knowledge and their alignment with his idea of a multi-layered existence.
No multi-layered metaphysical construct in the ancient world discussed simulations. There isn't even a vocabulary that could describe an abstract simulation rather concrete reenactment, like drama or a physical model.
Some ancient religions spoke of the physical world as an illusion, but that too does not mean anything like a simulation.
A simulation is a virtual reality created by a higher intelligence in a real-world environment with great real-world power. Plato's forms weren't discussed as beings who did anything, and in the end were just reifications of predicates.
Descartes' skepticism is the foremost example of a simulation issue, but in addition to the great flaws in his arguments in the Discourses, saying you can't absolutely prove that your senses are not an elaborate deception is no indication that it is.
Profound ignorance and misunderstanding of philosophy is, for me, the most salient feature of the latest discourse on world-as-simulation.
2 weeks of an intro to philosophy college course would correct most peoples' thoughts on the matter, as examining Descartes is the most basic first step in learning philosophy.