I read a lot. I retain little of what I read, which bothered me for a long time until I worked out that retention isn't the point. The question is whether reading it changed something in how I see something else. That's the interesting/useful split, and I think about it a lot.
Interesting is easy. Most things are interesting if you approach it right. A Wikipedia article about a niche historical event. A documentary about a sport I don't follow. A long piece about how concrete is made. I find these things interesting and they make me, in some vague sense, a more textured person. They don't, however, help me do anything differently.
Useful is harder. Something is useful if it changes how I act, or think, or approach a problem. Useful doesn't have to be practical in a narrow sense, a novel can be useful if it shifts your frame on something you'd been stuck on. But the bar is: did this change anything? Did I enjoy it?
The problem with the internet is that it has made interesting things very cheap and useful things no easier to find than before.
The trap I fall into is treating interesting as if it were useful. Consuming information as a proxy for doing something with it. Reading about productivity instead of being productive. Reading about travel instead of booking something. There's a comfort in interesting that useful doesn't offer, because interesting asks nothing of you.
I've given up trying to retain everything and started asking a simpler question when I finish something: did I want to tell anyone about this? Not to perform knowledge, but because it connected to something I care about. If yes, it was useful. If no, it was interesting, and I should stop pretending it's the same thing.
I also try to read less and sit with things longer. Which is harder than it sounds when there is always more to read.