Should there be a visible steam plume from the Apollo astronauts sublimation cooler in the lunar EVA videos?
As an example, during the Apollo 12 commander's first EVA (of 3 hrs, 44 minutes), 4.75 lb of feedwater were sublimated, and this dissipated 894.4 Btu / hr.
That's 2.154 kg of water over 224 minutes, or 10g/min, or 0.16g/s.
Water vapor is invisible to the naked eye (2, 3). What you see e.g. when boiling water is not the water vapor itself, it's small droplets of liquid water (fog, mist, steam) which are suspended in the air and carried by the air flow.
With only so little mass escaping the suits, those droplets do not form in any substantial amount, and there is no air that could carry them around. Thus, there is nothing to see.