Honestly, DuoLingo is one of the slowest and shittiest ways to learn a language. I think it’s a great supplement to a language learning routine, and a nice method to keep your habits going, but it’s borderline useless by itself.
That said, it 100% depends on your personal goals. If you’re planning to go to Japan sometime in the future and would like to be able to accomplish some basic interactions (ordering food at a restaurant, asking where locations are, etc.) but have no interest in becoming fluent, it could definitely serve useful.
Honestly it’s just become part of my morning routine and helps jump start my brain for the day. Learning new things is fun even if it’s not the most strategic approach to becoming fluent in a language.
Whether you’re learning anything useful is wildly debatable imho.
You should try clozemaster and lingo legend, I liked those a lot more :) with clozemaster you can even try your hand at speaking (though that feature is in beta and may be pay walled. I don’t remember, but the subscription was well worth it for me and the free features are enough for daily practice.)