It's just a matter on how much time you spend learning the language. Even if you only consider the time you spent in school merely learning your own native language those school lessons will add up to thousands of hours. How many adults, who have already "learned" a foreign language, dedicate 6 hours per week purely on further improving their skills in that language for 12 years? If you are worried about not knowing…
Where do you find the words to add to your deck? I add words discovered in lessons - which are great for a proper context - but using words from internet sources (the news, etc.) is time consuming and means I keep seeing words from a few narrow niches (politics, economics, slang) without any understanding of how they'll be interpreted.
Get used to it. Learning a language is time consuming. Nobody ever learned a language by studying it 30 mins per day.
At a beginner level, one can find words through the grammar textbooks and the like.
At intermediate+, you find words through material that you find. For example, news, tv shows, songs, and the like. It's up to you from here on out.
> I keep seeing words from a few narrow niches
The trick is to vary your resources. Read the news, but also read a short fiction book, watch a comedy tv show and then a drama, etc. You should also find resources at your level. If you are a beginner, don't bother reading the news. Even if you look up all the words, they're usually niche and will not help you that much.
One way to combat this is to find a list of the 2k, 3k, 5k most commonly used words and add them to your anki deck.
What I do is I add unknown words from my daily conversations with native speakers.
> without any understanding of how they'll be interpreted
If you see a word in a sentence from a native source, that's a pretty good way to see how it's used. You can also cross-reference with a dictionary or by asking the native speakers you practice with.
When you add a word to your anki flashcard deck, you need to also add sample sentences. It's borderline useless to learn a niche word without examples of how it's used.