I read mostly self improvement, business and psychology books. I also struggled with forgetting soon after finishing a book.
It seems some people only remember 2% of each book read. Some people don’t mind, but it really bothered me. I figured the best way to learn was to teach what I was reading immediately.
I started writing notes and then writing book reports and publishing them on a blog. I take all my notes in Google Keep so it’s synced across all my devices and easier to edit into book reports. It decreases the rate I finish books, but I’m synthesizing my thoughts and solidifying the contents in my long term memory.