Partly. While it's rooted in some real circumstances and people, there might be some artistic liberties and fictional elements added for dramatic effect.
One Night in Miami is somewhat true. It incorporates real historical figures and events but fictionalizes certain aspects to make it more engaging for the audience.
It's not a true story. Usually, such works are based on imagination and crafted to engage the readers or viewers. The plot and characters are invented to tell an interesting tale.