This is exactly what I have noticed as well. For example, when reading Designing Data-Intensive Applications for the first time I had absolutely no exposure to distributed systems and concepts like partitioning or replication. Even though it wasn't that difficult to understand the chapters, I couldn't truly appreciate the information.

Now, however, with more experience and the necessity to deal with these issues at work, I keep revisiting DDIA on a regular basis and this is when the book truly shines for me.

It just bothers me at times that even though I read quite a lot, the amount of information I can confidently restore even within a few days is not even close to 50%.

Taking notes is definitely something I should try, in addition to organizing a handy set of bookmarks in Raindrop whenever I encounter something useful.