In Humans, there’s a disorder called lissencephaly. It’s effectively just human brain but smooth and comes with significant developmental impact. It can be hard to define intelligence sometimes, but people with lissencephaly are behind pretty much no matter how you measure it.

For animals, it’s less clear because it can be even harder to define intelligence especially since animals frequently don’t need to be smart in ways that we would care to measure and sometimes even smooth brained animals are very focused on things we would classify as ‘intelligence’ from a human standpoint. We’re pretty confident on wrinkly brains in mammals being more efficient though and a correlation between efficiency and effective intelligence is usually a safe conclusion. The wrinkles basically just let you stuff more usable brain into a smaller skull.