Realizing that my prior separate advice wasn't as actionable or specific, I thought I'd take another crack at your question.
Some seem to miss the older techniques and names for this sort of practice and get too wound up in words like categories, tags, #hashtags, [[wikilinks]], or other related taxonomies and ontologies. Some become confounded about how to implement these into digital systems. Simplify things and index your ideas/notes the way one would have indexed books in a library card catalog, generally using subject, author and title.
Since you're using an approach more grounded in the commonplace book tradition rather than a zettelkasten one, put an easy identifier on your note (this can be a unique title or number) and then cross reference it with any related subject headings or topical category words you find useful.
Here's a concrete example, hopefully in reasonable detail that one can easily follow. Let's say you have a quote you want to save:
No piece of information is superior to any other. Power lies in having them all on file and then finding the connections. There are always connections; you have only to want to find them.—Umberto Eco, Foucault's Pendulum
In a paper system you might give this card the identification number #237. (This is analogous to the Dewey Decimal number that might be put on a book to find it on the shelves.) You want to be able to find this quote in the future using the topical words "power", "information", "connections", and "quotes" for example. (Which topical headings you choose and why can be up to you, the goal is to make it easier to dig up for potential reuse in future contexts). So create a separate paper index with alphabetical headings (A-Z) and then write cards for your topical headings. Your card with "power" at the top will have the number #237 on it to indicate that that card is related to the word power. You'll ultimately have other cards that relate and can easily find everything related to "power" within your system by using this subject index.
You might also want to file that quote under two other "topics" which will make it easy to find: primarily the author of the quote "Umberto Eco" and the title of the source Foucault's Pendulum. You can add these to your index the same way you did "power", "information", etc., but it may be easier or more logical to keep a bibliographic index separately for footnoting your material, so you might want a separate bibliographic index for authors and sources. If you do this, then create a card with Umberto Eco at the top and then put the number #237 on it. Later you'll add other numbers for other related ideas to Eco. You can then keep your card "Eco, Umberto" alphabetized with all the other authors you cite. You'll effect a similar process with the title.
With this done, you now have a system in which you don't have to categorize a single idea in a single place. Regardless of what project or thing you're working on, you can find lots of related notes. If you're juggling multiple projects you can have an index file or document outline for these as well. So your book project on the History of Information could have a rough outline of the book on which you've got the number #237 in the chapter or place where you might use the quote.
Hopefully this will be even more flexible than Holiday's system because that was broadly project based. In practice, if you're keeping notes over a lifetime, you're unlikely to be interested in dramatically different areas the way Ryan Holiday or Robert Greene were for disparate book projects, but will find more overlapping areas. Having a more flexible system that will allow you to reuse your notes for multiple settings or projects will be highly valuable.
For those who are using digital systems, ask yourself: "what functions and features allow you to do these analog patterns most easily?" If you're using something like Obsidian which has #tagging functionality that automatically creates an index of all your tags, then leverage that and remove some of the manual process. The goal is to make sure the digital system is creating the structure to allow you to easily find and use your notes when you need them. If your note taking system doesn't have custom functionalities for any of these things, then you'll need to do more portions of them manually.