After 4 months of Duolingo, my literacy in German is still extremely limited
There are plenty of threads here discussing Duolingo, and some have details on what to use additionally. Use the search function.
Duolingo alone won't get you past basic German (as you've noticed), and can also lead to bad habits for language learning.
More on reddit.comB1 to B2 in 4 months?
Absolutely doable. I support most recommendations - here's my two cents:
Comprehension is the thing. You learn a language by understanding messages in that language, and nothing else. (That's the gist of current language acquisition theory, not just some hearsay.)
This implies: Make sure that you focus on stuff that you like and that you understand. If you need to do too much looking up, find something else. As long as you're B1, that excludes a lot (but not all) of authentic sources like TV, movies, even newspapers or Slow German. Those limitations will not last long though.
Don't wast time on "grammar", "drills" and "practice" or systematic vocab learning. If you like, buy yourself a grammar reference, not a practice book. When you've discovered things that need clarification, look them up. You'll see that this doesn't take long.
For now, DaZPod, a podcast specifically for German learners, could be an ideal source for you.
On speaking/communication: Simply try not to speak English/Spanish. At all. If that's too hard, set aside certain times during which you communicate in German only.
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