Igloo can generate (fully) on ice (or water below). Can include a basement shaft through water and the shaft filled with water, while the basement itself has air.

To reproduce

Seed 109324
Coordinates 700, 60

Observed

The example case igloo has been generated completely either on top of ice or water, though there is land 1 block away from it. It is on snowy plains biome-wise mostly, few blocks on frozen ocean.

The igloo even has the shaft down to basement going through the water. The shaft has water in it, yet the basement has air.

Expected

Igloos would not be created on ice/water. At least some area of its surface part should be on original land (the rest of the bottom could be filled with solid blocks like village structures do). Preferably the area that would have the shaft to basement would be on solid ground.

Also (or if igloos on ice is an intended thing), a basement (and its shaft) should not be generated if it has to go through water. Alternately, if it needs to go through water, the shaft should have air in it, not water. Or, if shaft is filled with water, the basement should also be filled with water (and the villager not existing, the zombie turned to the underwater version.)

Screenshots

Attached 2021-10-24_11.44.55.png and 2021-10-24_11.45.29.png