Is that still the case? IOMMUs have been a thing for a very long time, and nowadays you don’t trust random devices anymore. Certainly a Thunderbolt port (which is PCIe-via-string) does not want to expose memory unrestricted, and while you might be tempted to think that a built-in PCIe card could be under more lax policy because it’s considered “physical access”, you don’t actually want the driver code for that card to be a wide open attack surface for the rest of the system.