Personally, I never found Duolingo to be a great app for learning a language. By far the best combo I’ve ever found is following along with Language Transfer [0] lessons and reviewing flash cards using Anki. Adding in-person classes to the mix greatly boosts that.

I’ve learned more Greek in 2 years now with that combo as an adult than I did in a decade learning Spanish as a child by only taking classes. The only thing more effective was living in a city that only spoke the language I was learning after I had achieved a certain level of proficiency.

Duolingo made me feel like I was learning a language and having fun while doing it, but every time I looked back on using it, I observed I really wasn’t learning very effectively with it. It’s far too robotic and impractical in my experience.

[0] https://www.languagetransfer.org/