From what I understand water ice feels most likely, CO2 ice usually forms at much higher altitudes where we see the noctilucent clouds after sunset.

The speed the clouds are passing (see the timestamps) I’m assuming they are probably not at the elevation where we see CO2 clouds, but that’s just a feeling

I’ve read research that point to the water ice crystals seeding on minute grains of dust suspended in the atmosphere, so there could be some dust in the cloud as well.

I recall previous clouds observed by Curiosity being posted by JPL that were said to be water ice based on the altitude of the clouds which they had deduced from the windspeed

I’ve looked at the later images acquired on the same sol, even those looking at the crater rim wall (link) and I see no evidence of elevated dust levels (compared with earlier sols), so I feel they are probably just early morning water ice clouds just rolling on by :)