I worked for several years in a library with a very good children’s section. It often seemed that young boys were rather more interested in non fiction about something they were keen on - e.g. dinosaurs, creepy crawlies, space travel - as long as there were lots of pictures to go along with the text - text in a good sized font - rather than fiction, though I have known mothers insist on fiction books as well, as if NF somehow didn’t count as reading.
It never seemed to be such a problem with girls, but it did often seem that more books were aimed at them - e.g the very popular Worst Witch series.
As regards fiction for young boys, something really funny and v likely seeming rather too easy, was often the way to go - lots of dense print and few pictures was a guaranteed way to put them off. The likes of Horrid Henry, Captain Underpants or Flat Stanley often went down very well.
To me it doesn’t matter what they read, as long as they can be induced to read something, anything, and enjoy it, rather than thinking of it as a chore.
The Horrid Histories are very often a hit with older boys who look on reading as a chore. Ditto fiction such as The Demon Headmaster, but again, something that might seem too easy is always better than the other way round, if they’re reluctant.