I read 20+ books a year. I don't finish most of them, re-read some chapters from the old books. I underline stuff and I go back to the underlined things at the end of reading a book. I prefer reading hard copies and at any point if I've to look at the page number, I realise that the content is not worth the time. I skim through. If I still don't find it interesting. I leave it. It's okay to leave a book in the middle. Most books have a single point to make and the entire book is about examples around that point. If you understood the point already, there's no need to dig in further.

It's human tendency to forget things. So re-reading stuff I find valuable helps me more than reading lots of new books.