It depends on the car, my first car used gasoline, so the idle torque was low and you really needed to push the gas at the same time, otherwise it would stall, maybe not if you are releasing the clutch extremely slow, but that is not practical.
My current diesel car has so much torque even at idle that you really don’t need to press the gas pedal while releasing the clutch.
In an automatic the car decides when to shift gears and to which gear. And it also decides how softly or hard it should do this.
In a manual car you have to do all of this yourself, but that also means you decide when and how to do it.