If you want to read to learn you need to make notes, smart notes.
By writing what you have come across in your own words forces you to confront your understanding of the new idea/concept. You will quickly have a feedback loop which tells you if you have understood what you have learned.
Reading, reading, underlining, making notes in the margin of your book does not give you this feedback loop. It is as if you are simply nodding along.
When you try to put it in your own words is a different proposition entirely.
This is central to the Zettelkasten/smart notes system of acquiring and managing knowledge.
P.S. I am writing this short note from Rue l’Arc de Triomphe.