If you devote a couple hours a day to it you can acquire significant proficiency, just like with a classroom setting. But just like with a live course, merely participating and doing the homework will not be enough to achieve conversational proficiency. You need to do a lot of off-curriculum study/practice with a lot of different resources (some of them ideally real people with high linguistic competence).
Edit: I say this from a theoretical vantage as someone who studied applied linguistics in undergrad and from an anecdotal perspective as someone who did enough Duolingo over the span of a couple months to start reading news articles in Spanish with little need to consult translators/dictionaries but who still couldn’t navigate their way around a Latin American city. It took me a couple of weeks in Latin America to begin to communicate fluidly (still more time for conversationally) with locals despite the strong syntactic and broad semantic base heavy duo use afforded me.
Edit: I say this from a theoretical vantage as someone who studied applied linguistics in undergrad and from an anecdotal perspective as someone who did enough Duolingo over the span of a couple months to start reading news articles in Spanish with little need to consult translators/dictionaries but who still couldn’t navigate their way around a Latin American city. It took me a couple of weeks in Latin America to begin to communicate fluidly (still more time for conversationally) with locals despite the strong syntactic and broad semantic base heavy duo use afforded me.