Yes and no, technically, in an ion thruster, the gas is still pressurized and let out for propulsion. Its just that after the gas is initially pushed into the thruster, we rip off electrons to make the gas into positive ions which can be further accelerated by an electromagnetic field potential before getting ejected.

You are getting thrust from the depressurization but also from the electromagnetic acceleration of the thruster. The point is that it is more thrust than you’d get from just gas expansion alone and it still would provide basically no delta v for such a massive object.