Hostile mobs can spawn on ice, despite it being a transparent block. Tested in the overworld and end, and hostile mobs do spawn (see attached images).
Found a similar issue from 5 years ago (MCPE-25869), however that issued was marked as resolved and "cannot reproduce".
Here is a reddit post from a couple of hours ago, which lead me to test this behavior: reddit.com/r/Minecraft/comments/110lu91/why_are_endermen_spawning_on_ice_a_transparent/
Linked issues
is duplicated by 2
relates to 1
Attachments
Comments 2
Top slabs also allow spawns while being transparent/non-solid blocks. These are specially coded exceptions to the general rule that mobs only spawn on solid blocks. Moreover, polar bears are specifically coded to only spawn on ice in the frozen ocean biome so that mother bears and cubs will not get separated on the icebergs: see MCPE-105221. So I think this is working as intended.
Ice is also used in a lot of mob farms because of its unique properties of allowing spawns on top and spawn collisions on the side, and also heavily reducing light levels.
ItsDaCreeper
Isn't this a feature?