Chickens are dumb AF not only for how we rate human intelligence, but also against all the different tests and methodologies we have to try and objectively assess animal intelligence. I don't think they are capable of really having personalities so much as a few different ingrained behaviors that differ based on genes.
It is likely that the modern optimized broiler or layer chicken breeds are much dumber than the breeds that were common earlier. It is known that most domestic animals have smaller brains than their wild ancestors and this is likely to be even more so for the more recent breeds. (Even the recent humans have smaller brains than their hunter-gatherer ancestors, presumably due to the less challenging modern life styles.)
The chickens raised by my grandparents, with which I was playing when I was a small child, had very distinct personalities. Each one of them was easily recognizable. Some appeared to enjoy to interact with me and they were very curious, while others were shy and they would run away from any human.
They were roaming freely over a very large yard with abundant and varied vegetation and insects. They were exploring it all day long, finding various kinds of food for themselves. They received from humans only a food supplement, a shelter for the night and some nests for laying eggs.
I think chickens can have different combinations of behaviors, but I don't think they are complex enough to have personalities. For example, I don't think they are capable of reason, which is a requirement for personality according to the APA definition [0].
