This claim is completely true. Via the Statista website it shows how Duolingo is around 14 times more downloaded then any other application. Duolingo sits at 14 million while the next leading app is Lingutown at 1.9 million as of July 2024. One of the big ways that keep having people download this app is thanks to their very impressive business model. In a BBC report two of the top people "Von Ahn and Hacker developed a hybrid business model that combines ad-supported access and "freemium" elements, while also offering a paid subscription with extra benefits, like an ad-free experience and a family plan". What this business plan allows for is people don't feel forced to use another subscription which can be a big turnoff for many but that they get to still get more work done with minimal adds that they don't mind. But if they do wish to pay the app will then become even better for them.