Short answer: there is no convincing evidence that psilocybin from mushrooms or truffles raises GLP-1 or acts like a GLP-1 agonist. The appetite drop many people notice during a psychedelic experience is more likely tied to serotonergic effects, especially 5-HT2A activation, which can shift attention away from food and reduce food reward.
Both GLP-1 drugs and psychedelics can feel similar because they influence overlapping brain networks for appetite and motivation, but they do so through different pathways. For a concise primer on psilocybin and its context, see this overview.
In the other direction, GLP-1 medicines may slow stomach emptying, so some users report a delayed or weaker effect from oral psilocybin. I cannot verify a consistent interaction, and robust human data are not yet available.
Bottom line: psychedelics likely have minimal direct impact on GLP-1, and the overlap in appetite effects is mostly functional rather than mechanistic. Hope this helps.