Have you tried knowledge-graph tools like https://roamresearch.com/, https://obsidian.md/ (or) their self-hosted/open-source alternatives like https://github.com/athensresearch/athens (or) https://joekroese.github.io/tiddlyroam/ ?

They're far better than normal spreadsheets for research purposes and for retention I haven't heard anything better than spaced-repetition as I've mentioned in /comments/1137 . Perhaps a knowledge graph + spaced repetition tool is what you're looking for?