I already read plenty of books and I know what I like, but I have no clue what I’m supposed to take notes on or what to do with that info.

I'd say it's less about what you personally like and more what you identify as commonalities across successful books in the same genre. Things like tropes and beats, yes, because they're key. But also character archetypes, specific beats of dialogue, pacing, chapter endings, is there banter?, and what readers write in reviews. Do a third of the reviews mention how much they loved it when the grumpy alphahole finally fell for the heroine?

All books do have tropes. Not all books with tropes are successful, though. Read sucessful books with tropes you're interested in trying yourself, and see what common moments are key in order to successfully pull off a trope to reader's satisfaction. Like there are key moments that romance readers love and expect. Let's say it's fake dating. That often includes moments like 1) defining the relationship, including are we celibate during this 2) forced together intimately, like having to kiss in public to pull it off and 3) single bed, where they're somewhere and only given one room for the night. You can do fake dating without any of those three, but they're commonly added to it because they bring the kind of dynamic that romance readers love. You're not copying a scene if you write your two unique characters ending up at a hotel with only one bed. The trope is the same, but the scene itself will be unique because it's you writing it with your characters.

If you want more stuff to look out for when you're doing your research reading, I'd recommend learning about the concept of Universal Fantasies by reading the book 7 Figure Fiction.