Thanks for your reply!
You are right that SharePlay doesn't work entirely on the simulator, however the virtual FaceTime feature allows to create (simulated) spatial persona entities, as seen in the screenshot.
Because I originally found the issue while testing on the real hardware, it can't be just caused by the simulator.
Reproduction:
loading the sample project
start the simulator
open a virtual FaceTime call (via ‘features’)
activate the Spatial Persona function for the call via the FaceTime interface
build the example project on the simulator
start the SharePlay session via button