www.ncbi.nlm.nih.gov/pmc/articles/PMC8819838/ that still seems to find it may be more the human influence on a breed(or mixed breed dog as it were) than manifested in the breed itself.
An important finding was Pit Bull-type dogs in our community sample, as a group, were not more aggressive or likely to have a behavioral diagnosis than other dogs. As the nascent field of canine behavior advances, it will be important to better account for human influences on dog behavior. Our results showed genetic screening of canine behavior is feasible and suggest it may be useful for owners, breeders, shelters, working dog institutions and veterinarians.
If you were to compare the findings of the direct connection of anxiety, many smaller dogs have this but we as large humans tend to dismiss this in smaller dogs. The only reason we really focus into the pit bull is the association we’ve developed and the size. Also larger dogs are usually trained in defence. Less so with smaller dogs which also suffer with anxiety. No doubt a lot of owners get the ideal that they want to get a pit bull to install fear into other humans as a form of protection. this is a human introduction of a behavior.
Anecdotally my family owned many dogs. Sometimes we’d get a litter where two dogs behaved very differently to each other. We inherited many dogs with behavioural problems because of human error and the breed didn’t make a difference so much as size definitely did amongst the decisions many people made. No one wants to keep a large dog with behavioural issues. Why people associate it with pit bulls is mainly because statistically they are more prone to treat that particular breed (and in many cases any breed that looks associated to the pit bull) in such a way that installs more anxiety. That is a human error. Not a breed error.