Why does my 2019 Toyota Kluger use so much oil?

It would seem very strange to me that an almost-new Toyota V6 engine would be burning oil to the extent that a new short motor would be required. And it seems that wasn’t the problem anyway, but I agree that more than a litre per 1500km is too much. Had the short motor (pistons and piston-rings) been the problem, the new short motor should have fixed it, but a leak-down and compression test should have given a few clues, too. In any case, the dealer should now be looking for the real source of the problem. I’d be starting with the valve-stem seals or valve guides which are part of the cylinder head and aren’t replaced when a new short motor is fitted (because the original cylinder heads are retained). I’d also be checking the operation of the PCV (crankcase ventilation valve) which can also make oil disappear if it’s faulty.

As for your next step, well, thank goodness for new-car warranties, eh? Basically, you’re covered whatever happens because that’s how warranties work. It’s up to the dealer to decide what steps it takes from here, but while ever the dealer is trying to fix the problem, you need to give them the chance to do so. It would be nice if you were provided with a replacement vehicle while yours is being assessed or fixed, and I’d definitely be asking for that much. Have you contacted Toyota Australia’s customer service number? Sometimes you’ll have a quicker resolution if head office gets involved. The other option if you’re really unhappy with how things are progressing is to contact the ACCC.