This word seems to have a bad connotation, at least in my past it did. Thankfully I haven’t heard this word used today, at least where I live. Growing up I heard adults use it to describe stray dogs. There were many abandoned animals, usually cats or kittens “dropped off” at our farm. We lived quite a ways from other neighbors, so it was a convenient outlet for unwanted animals.
One of my favorites was a small black dog I named Kim. I had no idea of her heritage, so I suppose mongrel might have been an apt, if not harsh, description. She was my first pet. I later lost her when an unfriendly “neighbor” shot her in the woods on our farm.
I’m sure she’s not a “mongrel” up in dog heaven.