I studied Spanish all through school and continued at the college level, but I can say I didn’t really learn the language until I had the chance to live in Latin America, avoiding English-speakers as much as possible. And reading, and consuming telenovelas daily for years.
Since then in the last couple of years I tackled Portuguese via Duolingo. It’s a good tool, it gives it to you in baby steps, I did it in small bites to not burn out. Having finished the course, again I started reading, the New Testament, then novels, re-reading the first several. I’ve read now a dozen or so. It’s a slog but easier on re-reading. And listening to Portuguese speakers on YouTube at least a few minutes each day. My ear is still not tuned, so listening is a struggle. But some YouTubers are easier to understand than others, and I keep at it.
I know I will not master the language without actually visiting a Portuguese-speaking country and going through the same process I went through learning Spanish. But it’s doable.
The New Testament in a target language is my favorite language learning tool. Every time I read Holy Writ for the first time again, I see facets and nuances I never noticed before! For example, the Turkish phrase kendine keni (he, to himself) opened my eyes to the fact that it was the villains of our Lord’s parables who talked to themselves!
e-sword.net provides an excellent free resource for the Bible in 100+ languages.