Harvey (1996)

An unlikely hero, Elwood P. Dowd. This mild-mannered-but-eccentric bachelor has, for several years, happily kept company with Harvey, a six-foot-tall rabbit that only he can see. All's well until Elwood's social-climbing sister, Veta, and her teenage daughter, Myrtle Mae, come to live with him and fear his odd behavior will undermine their ambitions. When Elwood disrupts the ladies' first afternoon tea party by introducing wealthy Aunt Ethel Chauvenet to Harvey, Veta sees that something must be done right away. She takes compliant Elwood to the Chumley Rest Home, leaving him in the car while she tells a Dr. Sanderson all about Elwood and Harvey. Sanderson concludes that Veta is the psychotic one and has her carted off to be committed. Meanwhile Elwood is treated with respect and dignity in light of his sister's mental state. When Dr. Chumley, head of the rest home, returns and hears of the case, he draws the opposite conclusion-that Elwood in fact hallucinates.

Unfortunately the movie Harvey is not yet available on HBO Max.