Sometimes with the most popular of books, chapter-by-chapter summaries are available. I will read those if I've been away from a book long or just have questions about what I read.
https://asimov.fandom.com/wiki/Foundation
https://bookanalysis.com/isaac-asimo.../plot-summary/
These two seem to have decent summaries.
I also use the "search in book" feature, highlighting any name I don't recognize and searching to see the first few times it was used to remember who the character was