Caleb Rivers, the name on the pill bottle found in Noa's mom's purse, is a reference to an original Pretty Little Liars character.
One of the characters works at a law firm called Strode, Prescott, Ripley associates. This references Laurie Strode from Halloween, Sidney Prescott from Scream, and Ellen Ripley from Alien -- three lead characters from horror films from the 1980s and '90s.
Tabitha's film studies teacher is named Mr. Smithee. This is a reference to "Allen Smithee," a placeholder name which the Directors Guild of America used when a director wished to have their name taken off of a project.
References are made to the film Hereditary (2018), in which Karen and Kelly's actress Mallory Bechtel appeared.
The ballet instructor (played by Kate Jennings Grant) is called Madame Giry, likely a reference to the character from "The Phantom of the Opera".