Examples:

My father told me that when they were a little boy, they would help their friends with homework.

The bitch attracted so many dogs in the neighborhood. Now, they are pregnant with puppies.

"Father" is masculine semantically. But the pronoun they is used instead of he. This has nothing to do with the father's gender identity. The speaker just uses they pronoun for an obviously male person.

Bitch is feminine semantically, referring to a female domestic canine. Dogs in that context are male domestic canines. Males cannot get pregnant, so obviously, "they" is used to refer to the bitch.

More Examples:

I am agender. My pronoun is they.

I am male. My pronoun is they.

I am female. My pronoun is they.

Elizabeth is my girlfriend and a great cook. They bake the best cookies.

See that man over there? They sell street food.

Another Example:

And so, they said...

Is your teacher male or female?

Male.

Go on.

And so, they said...