What about low frequency vocabulary? I'll never encounter it enough times to acquire it from input.

This is a common misconception. You actually will encounter low frequency vocabulary very often. This assumption that so-called “low frequency vocabulary” can’t be learned from input arises from the belief that because a word is not very common, we are only likely to encounter it once in a very long time, and therefore not encounter it enough times in a short period to be able to memorize it. The problem with this reasoning is that it assumes that in each source of input in the language, the frequency of each word follows the same frequency than in the language overall. This couldn’t be further from the truth. Besides the most basic grammatical connectors, the vocabulary used in different situations in which the language is used varies wildly. You will see very little overlap between a Wikipedia article, a daily conversation, a newspaper, and a fantasy movie. The frequently used words in those contexts are completely different from the frequently used words in the language overall. Every area of use of the language has “low frequency” vocabulary specific to that area that gets repeated a lot. Even within an area, each topic has its own specific vocabulary. Even within a topic, every author or speaker has their own words they use more often. Every context in which the language is used has its own “low frequency words” that are actually used very frequently in that context. Learning “low frequency” vocabulary is actually unavoidable. Every time you are consuming comprehensible input, that input will belong to a specific area of usage of the language, a specific topic, and will have been produced by a specific person or group of people. If you feel like recently you haven’t encountered many new words, try reading books by a different author, explore media formats that you haven’t consumed yet (documentaries, reality shows, ...), or learn about a topic that you would like to know more about.