I’ve used Anki for language learning for several years, and I’m consistently surprised by what I can recall, and how that directly translates to reading content in that language.
For books, I’ve been using Readwise for at least a year as well — it will surface highlights to you in an SRS-like manner each day in a more lightweight way.
I agree with some of the other comments I’ve seen that we don’t need to remember everything. The author says they tried Anki, but dropped it because of the sheer amount of review it would require. But this is the point, in some sense. Studying with spaced-repetition is effective because it is tedious. So I’d only recommend it for information you really want to internalize, or languages.