imho, #duolingo was always shit that i ran a mile from. it trivialized the experience of language learning and talked down to users, gamified acquisition and treated people like babies. its design was ruined by being based around how apps/computers work, it was one-dimensional. (feel free to disagree without trying to change my mind.)
everyone has different brains and learning styles, but what worked for me a million times more effectively than duolingo was Assimil, originally LPs and books, now available as pirated PDFs and mp3s from your favourite torrent site.
Assimil was made by pedagogues who were clearly experts in language acquisition. it doesn't rely on infantilizing repetition, understands that the real name of the game is engagement (not the viral app/social media/notification kind), which generates (deep) attention and leads to things making it into long-term memory.
it works because you want to learn what they're talking about, you want to grasp the world that they're giving you increasingly complex glimpses of.