Just keep your cat inside, it’s not difficult. If the owner lets it out they’ve put it and the native animals around it in danger.
Letting a pet cat outside reduces its lifespan just by risk of being hit by a car, being poisoned, being caught in animal traps, etc.
That cat also kills several other animals, each with just as much value as a cat. Endemic species that actually belong there.
No, the mouse has more. It isn’t invasive and actively destroying the environment due to being introduced into a foreign habitat by humans.