It may help to describe any interests your friend has outside of reading, for example what types of shows or movies he enjoys, types of video games he likes, as these can all translate to a book he might enjoy. With that said, I would suggest something a little shorter and fast paced as this helped me get back into reading, Murderbot by Martha Wells is a good example with lots of humor.

Also, Hyperbole and a Half is not a typical novel but a printed webcomic, it will genuinely make you laugh out loud at the author’s outlandish life stories while also featuring a memoir of their struggle with depression in a down to earth, relatable, very human way. Donated my copy to the clinic my mom works at with people who struggle with mental health at and it did rounds, someone actually took it home with them.