I used to save everything to "see later" and get lost like you described, but instead I now host a TiddlyWiki locally where I transform what I see in a wiki reference (or discard).
Doing that allows me to filter out things that are temporary (news, opinions, etc) from things that might be useful later (book recommendations, cool projects, etc).
The big trouble remains in timeboxing this practice so it doesn't take a lot and become a problem again.
(I think the biggest lesson I took from that is that most of what we see that is important is time-insensitive. So, doing this work of saving and categorizing over a batch of content in a weekend hour is just fine)
Do you have any suggestions on where to read about the power of focus?
I don’t know about the whole learning only about what you’re focused on approach. I’ve often found valuable insights and lessons in places I wouldn’t have looked at if I were optimizing everything with this level of zeal.
Survival of the fittest, you always compare it to the rest and if it's good enough, it goes in and something else comes out?
I don't allow myself to bookmark "read later" pages again. I have to options: either I read the page here and now, devoting my full focus and attention, or it's gone forever.
I suggest you read about the power of focus, and also work on the damage that the fear of missing out is causing you. Yes, there are millions of interesting topics and insights out there, but you can only read one at the time. So ask yourself: "if I had to learn about one topic today (or this week), what would that be?". There is no later, there is no tomorrow... it's either now or never!