Setup and learn how to use Anki to practice spaced repetition. Going forward you can now decide what you would like to remember (so long as you are willing to spend 5-15 mins a day reviewing)! People's names, that command you always look up, your credit card number, interesting statistics (e.g number of passenger miles per death for bicycles vs cars vs planes) foundational facts in your field that will allow you to ponder and recognize them over and over (e.g multivariate Gaussian distribution).
Anki is the compound interest of learning. It makes learning far more rigorous and less stressful and makes it possible to remember things years after you've initially memorized it.
There's also Quizlet which is similar but I find it better because you can preview entire pre-built card decks on it which makes it searchable on google
Quizlet is great if you're looking for pre-built decks, as you mentioned. As far as I'm aware, there's no spaced repetition feature, which is the main value in Anki.
Also, one of the values to me in using Anki is creating the cards myself. It allows me to mull things over and decide what part of a fact is important, and how I'd like to recall it.
Relatedly, the value isn't necessarily in reading someone else's study guide before a test, it's in creating your own study guide. That process helps you understand and retain the material far better.
Like you, I used to think that creating my own decks is better than using someone else's.
But then I listened to a podcast episode, by The Learning Scientists, in which they say that research evidence shows that your time is better spent doing only retrieval practice (reviewing flashcards) than creating cards + retrieval practice.
Retrieval practice and spaced repetition (which is what one is doing when reviewing cards with Anki) are the most effective methods for learning for which we have strong evidence, according to the same podcast.
You can pretty easily search for quizlet decks and then import them into Anki so long as you don't need two-way automatic sharing. Google for extensions, depends on Anki version
I just realised that, years ago, I have used a paper-based version of Anki technique to massively increase my vocabulary in a foreign language in a very short time span.
https://apps.ankiweb.net/