Duolingo is great for producing a cursory introduction to a language. But yes, there is no substitute for immersion. For example I spent some time in Spain after learning the language basically on Duolingo. I’m sure I spoke like a 2 year old, but at least I wasn’t totally helpless (I was even able to give someone directions to the airport!). Contrast that with my experience in France where I barely knew anything, and felt totally out of place and awkward.