According to MacRumors, TikTok is the first non-Facebook app to reach 3 billion downloads.
“Sensor Tower Store Intelligence data reveals that the app, including its Chinese iOS version called Douyin, was the most downloaded and highest-grossing non-game app globally in the first half of 2021, reaching 383 million first-time installs and an estimated $919.2 million in consumer spending.”
More details here.