With more than 400 million viewers, Formula 1 is one of the most popular sports in the world. Yet for many years it was all but unknown in America.But reality TV changed all that.Since the Netflix series “Drive to Survive” — featuring behind-the-scenes footage of the usually-secretive racing teams and the sometimes contentious relationships between drivers and team executives — debuted in 2019, the American audience for Formula 1 has skyrocketed.Netflix doesn’t publicize viewer data, but the audience for ESPN’s coverage of Formula 1 races has nearly doubled — up to 1.5 million views per race — since the show premiered.According to a recent Nielsen study, Formula 1 is on track to top a billion worldwide fans this year, with 77 percent of those new fans under 35 years old.“Without ‘Drive to Survive’ there would be no American F1 boom,” Kevin Clark, host of The Ringer’s F1 Show, told The Post.