When she awakens from the trance and looks at the time, the woodgrain pattern in the clock clearly forms a partial skull.
In the beginning of the movie, Jenn (Kate Siegel) states that she is waiting for an Uber driver named "Viola" that will arrive in 9 minutes; Viola is the name of the character Kate Siegel plays in "The Haunting of Bly Manor".
At some point in the movie, they mentioned 'Project MK-Ultra'. This project ran from 1953 to 1973 in the USA. It involved the use of certain psychoactive drugs combined with hypnosis. These experiments are deemed a failure and are useless in practice.