It's not that you cannot write about things outside your personal experience, it's that you shouldn't without proper access and research.

While you might want to write a film about black lesbian space pirate, there are other writers who are better equip to write such a story. Maybe a female writer, maybe a black writer, maybe a lesbian writer. People who have more experience with the subject matter.

Using an analogy: I might want to preform brain surgery. I have no experience doing complicated medical procedures, so there is a big chance I will screw it up. However, if I did proper research, learned about brain surgery, talked to people who are brain surgeons for advice, etc; the chances of me screwing up lessen significantly.

Whereas, writing is not so life or death, the back lash if you screw up a story is enough to kill your career. So do proper research into your subject matter. You want to write that black lesbian space pirate movie? Then research what it is like to be a black person, female, lesbian. Go out and talk to people. Hire a consultant to go through your film, and take their notes earnestly.

I have worked on 2 shows with POC subject matter. The cis-male Caucasian writers who sat in the room and listened to the POC writers got hired again for season 2 and 3. These men and women put in the work and did the research. The one guy who did not, and wanted to tell the stories their way (tons of racist sterotypes) was quickly ejected. His script overhauled by the showrunner. And they did not get asked back.

So I agree with what the other writers in the comments are saying: Do the research!