Yes, 'Once Upon a Time in Hollywood' is based on a true story. It weaves real - life events and figures from 1969 Hollywood into its narrative. For example, the Manson Family murders are a major part of the backdrop. However, it also takes a lot of creative liberties. Tarantino has a knack for blending historical facts with his own fictional elements to create a unique cinematic experience.
It's not based on true events. The movie blends various elements to create a fictional narrative set in the Hollywood context. The characters and plotlines are crafted for entertainment rather than being true to life.
Once Upon Hollywood is more of a creative work inspired by the era rather than being based on actual events. The characters and plot are crafted for entertainment purposes.