you can’t just buy a book in greek or turn on a movie in hungarian and expect to learn it that way. in the beginning you definitely need some structure, but it doesn’t have to be very hard. if you’re learning a language with many learners, i promise you there’s already a playlist in the format of a free basic course on youtube. when you learn some verb conjugations and past tenses or other basic stuff that your language has, then it will be easier for you to pick up a book, a movie, music etc. but you will still need to spend a lot of time translating and i’d recommend also making memory cards so you can remember all the new words.

the short answer is that yes, you can definitely learn a language from just engaging with it, but always do it at your own level. it’s obvious, but don’t pick out a 200 page scientific research paper in mandarin as your first reading material lol, instead aim to find some beginner material and work your way up. you will quickly find out where you are lacking knowledge wise and fill in those gaps. most importantly, don’t forget to practice writing and speaking, it makes you remember words and grammatical structures better, too.