I had a cat years ago that adopted us. (1975) Cats do that. We called him “gato de siete garras”. Cat of seven claws. He had two extra claws. He used them like an opposable thumb. He could pick up things with one paw. The first time he did this I said to myself, “a cat can not do this.” I immediately looked at his claws and feet. I then realized he could do this.
He was a good cat.
Around these parts, the extra claws and fingers are usually found in barn cats. Usually found on the front paws and are large enough to be seen as extras if one is looking.
Old buddy of mine used to have a cat with one very pronounced extra claw on each front paw. He named the cat “Hitch Hike”