I did.

I took 2 years of Spanish in high school. That had the same almost useless effect that it had on every other high school student, but it did lay some groundwork.

Over 10 years later, I achieved a conversational level of Spanish using maybe 80% Duolingo. It was inefficient, but the gamification kept me going.

I think it is now much less efficient than it was when I used it, maybe half as efficient, because the app is now hammering and testing every detail to an unnecessary degree, and they are also trying to increase usage time.

I am probably not conversational anymore because I haven't kept up with it. If I had to learn again I might try to incorporate only like 25% Duolingo. I'm not sure if that's possible though. I might just not use it at all.