I can concur. I have used 0w20 at the height of summer this June, in peshawar, under full load. I faced absolutely zero issues. Nothing at all out of the ordinary. The car ran well, throttle response was excellent and fuel average was quiet alright. These modern Toyota engines are designed to run with thin oils and if the dealership insists on thick, dino juice oils, then they're just looking for suckers to scalp, since they receive those oils in bulk and dirt cheap. Btw the car in question is a 2019 Corolla Grande.