There is no secret: learning a language is hard. It takes time and effort. If the question is "by doing one Duolingo exercise every day for 600 days, can I get

There is no secret: learning a language is hard. It takes time and effort. If the question is "by doing one Duolingo exercise every day for 600 days, can I get fluent?", the answer is "definitely no". But it's better than doing nothing for 600 days. And it's pretty damn convenient: you can do it while waiting for the bus or whenever you have a few minutes to kill (instead of swiping TikTok). But if you want to actually learn the language, it's not enough. You can keep using Duolingo, you just need to do a lot of other stuff on the side.