Suffer the same problem with reading. Best advice is to just keep going even if you feel like you aren’t retaining. It is okay to read it slower or even aloud until you feel comfortable stopping. Because you are retaining more than you think you are. It is not every excruciating detail, but it is enough for the story. You’re not reading to recite the whole thing back to someone, you’re reading for a story/plot/main idea. Also, if there is something you really like in a certain chapter, you could notate it in one form or another. Doesn’t have to be all the time, and it could be just that once to help you jog your memory for it. Very possible that ADHD is something you are dealing with like others have commented.