I've got through a lot of note-taking methods tbh. Even as I went through my university course, it's something that I never really got the hang of and was satisfied by (part of it is that I was usually too busy with the workload to really do a deep dive and perfect any particular one).

I've tried doing it on paper (or devices you can handwrite on) because of all the scientifically-supported benefits it gives you in terms of concentration and memory and so on, and I don't doubt those benefits, but ease of access and searchability and connectivity are just way too important to be flipping through papers as soon as your notes reach a certain size.

So I do it via keyboard, usually on a device that isn't connected to the internet to avoid distractions (with the PDF or epub predownloaded, or the book next to me if I have it physically). There's a lot of note-taking apps out there and they each have their own benefits; I found that I dislike pure memorization/flashcard apps like Anki because I do actually just need a big place with my notes not all separated by flashcards.

I found that I dislike various pure Zettelkasten-y apps like Obsidian. A Zettelkasten, literally "second-brain" is kinda like a massive decentralized mind-map which focuses on connections between pieces of information rather than maintaining a strict set of notes, if you're unaware. I found that I actually quite liked having the ability to have a place for all my notes from a certain book to just read through and not scattered around (and a Zettelkasten is kinda explicitly about not memorizing stuff because, y'know, your second brain is meant to have the information and not the brain in your head, but I quite like just memorizing stuff so I can use it without referencing a giant mindmap).

Notion is pretty good and I still use it for a lot of things. It's a fairly basic app where you can take notes but that also has functionality for to-do lists and tables and so on.

I think I like RemNote the most. There's a lot of complicated stuff you can do with it, but at its heart, it's a notetaking app where you can generate flashcards inside the app and it'll do spaced repetition schedules automatically, which is nice because there's some things that I would like to flashcard but definitely far from everything. I also just like the structure of the thing, it's been good to encourage me to break away from agonizingly long paragraphs and instead break them up into bitesize pieces that are nonetheless connected together.

But at the end of the day, the app used isn't really what's important, because it's very easy to trick yourself into thinking you're being productive by messing with settings and doing youtube tutorials about XYZ or TOP TEN TRICKS FOR PRODUCTIVITY, etc.

As for the strategy while taking notes, there's also a ton of them out there which boast wild success. Again, I don't think any of them are wrong necessarily, but there's a lot of them that feel either needlessly complicated/require a lot of extra thought ("oh gee, what do I colour-code this? is this categorized as a fact, an idea, a concept, or commentary in my elaborate classification highlighting system?") when you should just be thinking about the book and its contents, or they feel like they're designed for specific subjects; what works for literature analysis won't work for medical school, which won't work for mathematics, etc.

I think the best way I've found is to simply read through the book and try and summarize what the author is saying in your own words and add examples. There's really only three guidelines I'd go for:

1. Keep your paragraphs relatively short to keep your notes in relatively bitesize chunks of information and explanation

2. If you're ever just typing things in from the book verbatim for more than a couple sentences at a time, you've probably lost focus - you might need to take a break for like 5-10 minutes or check you actually understand and aren't just pretending to understand so you can get through the book faster. It's fine to repeat decent stretches because there's only a few concise ways of saying something, but make sure to break it up by at least changing a word or re-ordering a paragraph to make sure your brain is still actually doing stuff.

3. If you don't understand something, then don't just repeat it verbatim in your notes because you'll just confuse yourself later. This is where a lack of internet connection can be a real pain, so maybe keep it on if you're dealing with something dense and confusing

Sometimes putting things in your own words is actually longer and less concise but uses less complicated jargon so it's actually easier to understand overall. There's usually a lot of extraneous/unhelpful information or padding that can be removed though, so my edited notes are very often like a quarter/third of the size of the actual book, maximum.

You can edit them from there after you've read the chapter/book. Often, you'll find that the author goes back over ground already covered just to remind you, and you might not catch this while going through it (especially if it takes you a week or two to get through it). Other times, you'll find that information you wrote down just wasn't that relevant. Obviously we aren't studying for a test here, there's no chance it'll be on the "exam", so delete parts at your own discretion.

I think even if you go for more exotic notetaking things, it's better to just get raw sentences down and then go back over the notes afterwards with the colours and referencing and tags and such.

The whole process takes a lot longer than just reading the book without making notes - a frustratingly long time, even - but it means that you'll never have to read it again in your life, if done right, and you'll memorize much more of it (especially if using flashcards in addition), so it's much more efficient and time-saving over a, say, 30 year timespan.