I’ve met some lovely poos and doodles. Unlikely to be from health tested parents but temperamentally sound.
It isn’t just genetics which have an effect on a dog's temperament and behaviour.
Dam's hormones during pregnancy (cortisol)
Early experience
Environment
Gut microbiome, gut brain axis
Type of exercise
Sleep quality and quantity
Single event learning
Medical conditions
Pain
IMHO it is the owner’s role to be a “safe space” and to support their dog in times of stress – not cause it. Dogs deserve to feel safe.