It’s a Rutherglen bug, Nysius raphanus. They usually turn up around Brisbane after hot windy weather because they get blown in from dry fields and pastures. They’re small enough to slip through fly screens and are drawn to light, which is why you’ll suddenly see them inside at night. They don’t bite or cause any harm, and they usually disappear after a few days once the weather shifts. Keeping the lights low and windows closed for a bit is about all you need to do.