Certainly, exorcisms are performed. Sometimes, they bring about healing, too. Does that mean demons are real? Not necessarily: It could be that exorcism triggers a shift of belief in a person with a mental disorder.
My own view is in the hub Healing Demonic Possession, Mental Illness, and Similar Challenges. It suggests that there are multiple worldviews on the nature of mental illness and demonic possession, and how it can be treated.