Everything works. The question is how well it works compared to what (opportunity cost).

Soon you will start to find "Duolingo wrapped" posts on Twitter, and you will see that top 1% of active users spend ~5 mins / day avg. and learn a few hundred words.

Considering that to reach fluency you need around 8k words and 700-1000 hours of study + practice (depending on language, and assuming good mindset, methods, teachers and resources), I'd say that Duolingo does not work at all.

Duolingo is not for people that wants to learn a language, it is for people that wants to want to learn a language.