We have two cats, a brother and sister from the same litter. Both are very good-natured cats, but the male is extremely friendly and engages with people much more than his sister, who is somewhat more aloof in general.
He also seems to be extremely intelligent. He plays fetch- the cats have a number of these cat toys that are little plastic multicolored springs that they bat around and chase. The male cat loves it when someone throws the spring— he’ll chase after it at top speed, then bring it back and drop it at your feet. He’ll even initiate a game of fetch- many times I’ll be sitting on the couch, watching TV, and he’ll hop up, drop the spring next to me and look at me expectantly. I tell my wife he’s more dog than cat (not because I think dogs are smarter, because the way he engages with people seems very dog-like). And, like a dog, you will get tired of playing fetch before he does.
My wife discovered YouTube videos where cats have been trained to (adorably) ring a bell for kitty treats, so she ordered a bell. We wondered how long it would take for the male cat to figure out the bell trick. The answer was almost immediately. His sister? Not at all.
There’s also an egg-shaped cat toy that has holes that release cat treats when the toy is batted around. The way the holes are designed the treats don’t come out easily- it takes some manipulation to coax a treat out. The male cat will paw it in a very careful and focused manner, giving the thing a quarter turn at a time until he gets a treat. When he no longer hears rattling he knows it’s out of treats and stops playing with it. His sister hasn’t figured out the treat thing.
Now, I’m not trying to say that boy cats (or the male of any species for that matter) are in general smarter than girl cats, just making an individual observation of ours. And of course, an argument could be made that his sister is actually the smarter one, being too above it all to embarrass herself by interacting with dumb humans.