I worked as a language teacher for a while. You see products like Duolingo come along all the time. They're always accompanied by hype in how they will help you become fluent. It's simply not the case.

The products are not necessarily useless, but they only help some people make some progress some of the time. They never live up to the hype around them.

Language acquisition is a multifaceted endeavor which takes time and effort. Anyone who tells you otherwise is either misinformed or lying. (There are some outliers who can learn/acquire languages with great speed, but they're very rare.)