I think it's not unreasonable to point out that, at least for Americans (I'm guessing the largest user base of Duolingo), of the three options you listed, one costs tens of thousands of dollars for us (academic instruction), and the other is virtually impossible to do because we aren't part of a bloc of nations with border freedom (immersion).
There are a multitude, nay - infinite! number of online classes with teachers who will use "traditional", textbook-based approaches. [2]
Young Americans regularly go for 1-2-3 month trips to Italy, France, Germany, etc. American passports give folks a ton of latitude. You can stay in a hostel and eat cheaply - many thousands of people have done it.
I'm not saying it's easy, but I will definitely push back on the idea that it's impossible.
(and will also absolutely agree that the convenience of an app will be 10,000,000x more tempting to use than doing any of the above)
There are also a number of social media influencers (who probably were language tutors in a past life) that run online paid communities aka you pay to be part of their language community, and then have access to classes, zoom calls, etc.
They're harder to find / it's more difficult to immediately parse which ones will be good. But you can get a preview of "how they are" by consuming what they publish. For instance, for Canadian (Quebec) French, these are great:
https://www.youtube.com/@wanderingfrench
https://www.youtube.com/@maprofdefrancais
https://www.frenchwithfrederic.com/
I'm sure there are equivalents for French from France, and other languages. Searching "Learn {language name}" on YouTube/Instagram would be a good start.
Its really not that common outside of really wealthy people. Only 50% or so Americans under 30 years old even have a passport, much less spend months overseas. And that's a percentage that has gone way up over the years. In fact, its probably more common to find people that have barely even left the same state than have traveled in Europe, especially so for spending any appreciable amount of time in any particular part of Europe.
https://today.yougov.com/travel/articles/46028-adults-under-...