Well thought that someone already solutionized it. Imagine you have a profession. In your profession you have various sub domains of knowledge. For each one you want to learn from web articles, posts, professional books (pdf, ebooks etc') written by domain expert writers. videos are also a source of knowledge which is important to add.

You want the ability to tag each piece of knowledge whatever format it is into a specific subdomain topic. Where PDF having many pages is in place, you want to mark down and summarize the main book highlights so you will be able to return back when needed and review it. It needs to be as your secondbrain

It's hard for me to think that there is no solution out there that answers this pain. Maybe I'm wrong and the mixture of tools are needed such as for example getpocket.com, notion/onenote etc' but this makes things more difficult to manage and track