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In my experience, the majority of spoken English doesn't use very many words. This is a fact of language and is constantly harped on in a lot of language learning discussions.
That said, there exist an absurd amount of words in the English language and you will never learn them all. BUT, if you actually want to learn more words, I really think the only solution, for anyone, is to read. This doesn't just mean books on paper, you could also listen to audiobooks. Either way, the full richness of English (or any language) will only come through reading. This will sound arrogant, but I have a significantly better vocabulary than the rest of my family. I routinely drop words that they don't know. Which is a good feeling because I remember vividly often having to ask my parents growing up what new words meant. Now they ask me. The reason for this? I read. A lot.
You also don't only have to limit yourself to books. Periodicals, especially high level ones, are a huge boon to my vocabulary. Two I recommend enthusiastically are The New Yorker and The Economist. Both are written with high-level vocabularies. They are sometimes difficult for native English speakers (see the link at  for a discussion on Hacker News about the question of New Yorker's reading level in relation to CEFR levels).
If you are not ready to read The New Yorker or The Economist, do not worry. Just read. Whatever you want. Sci-fi is my favorite go-to guilty pleasure and it's perfect for starting out in French (for me). But any pulp genre work will work just as well. All that matters is that you read. As you read, you will naturally gravitate toward books that interest you, which will likely be where your level is. The result is, as you grow, you will read higher level material. Eventually, you'll want to read Shakespeare, or Tolstoy, or Joyce. See this video discussing The Power of Reading by Stephen Krashen, a beloved language acquisition expert in the polyglot community.