Why we forget what we read
Most of what we read online is gone within a week. We remember that an article was good, but not what it said, and the tab that held it closed long ago.
Highlighting helps only when the highlights come back. If they live on a page that changes, in an account that expires, or behind an export paywall, they are not really yours.
A useful habit is small: mark the one sentence that changed your mind, then review your marks once a week. The review is where the reading turns into knowledge.