Haven't seen Oppenheimer yet (though I certainly will), but here is my view on biopics:

From the audience's perspective, historical accuracy takes a backseat to relevance or relatability.

No one in the theater watching Oppenheimer experienced anything like the protagonist (the few people who shared some of Oppenheimer's experiences are all dead). So the goal of any decent writer creating a biopic of him is to make his central challenges / dilemmas relevant to the life of a contemporary audience. Same for a biopic of Abraham Lincoln, George Patton, Karen Silkwood, etc. etc.

More or less standard advice for writers starting out on a biopic is not to tell the entire life history of a figure but to focus on a small, significant period of that person's life. Such a focus naturally makes it easier to locate an overlap between the subject's life and the audience's concerns / experiences. It's fairly easy to incorporate a few flashbacks, symbols, etc. to refer to the larger lifetime of the protagonist (the motorcycle scenes at the beginning and end of Lawrence of Arabia).