Not every photograph of a person feels like a portrait to me. That has little to do with how professional the image looks.
A good photograph can be technically sound and still mainly record someone’s appearance. A portrait becomes more interesting when something of the person is visible too.
It does not have to be a revelation
I am not looking for a hidden truth. Often the difference is much simpler: the way someone looks, a posture that comes naturally or a little tension in the face.
The same applies to a dog. A characteristic posture can say much more than a perfect sit straight towards the camera.
Technique should recede
Light, focus and composition matter. They should be reliable enough not to come between the viewer and the subject.
But technique alone does not make the portrait. The photography works when it draws attention to the person or animal rather than to itself.
Recognition
The best compliment I can receive is not that a portrait is beautifully lit. It is when someone says: yes, that is him. Or: that is exactly her.
That is where the difference between a photograph and a portrait begins for me.