I read a lot of science fiction, and a younger friends at work frequently asked me for recommendations, and he liked talking about the books after reading them. At some point I found out that he exclusively consumes them as audiobooks, which is fine and I didn't think much about it. Some years down the line, when I was getting ready to retire, I had to pass on things to him. There was enough of it that, in addition to working elbow-to-elbow with him, I documented all the details in some long emails. When we meet, I'd say "The details are in the email," and focus on explaining the big picture.
It became obvious that he never read the emails. When I talked to him about it, he admitted that he really struggles with any long block of text. The guy is really smart, and he knows a lot about a lot of things, but he gets all his info from audio and video because struggles to consume text. There's clearly some kind of learning/mental issue going on there. It's going to make the job tough for him, but I hope he works it out.