The word مِن can have a couple of meanings, so the verse can refer to different things.
The verse translated with مِن replaced with "from": ⟪Allah sends down from the sky from mountains in it from ice⟫
Everyone agrees ⟪from the sky⟫ refers to the direction and origin. Meaning, it comes from the sky.
⟪from mountains in it⟫ can be understood in three ways:
Direction and origin, like the sky. So, the meaning would be ⟪Allah sends down from the sky, specifically from mountains in it⟫. In that case, the mountains would refer to the clouds.
Partiality. So, the meaning would be ⟪Allah sends down from the sky parts of mountains in it.⟫ Maybe this refers to the hail or rain as parts of the mountains.
Simple connection to the verb. So, the meaning would be ⟪Allah sends from the sky mountains [that were] in it⟫. In this case, the mountains are the ones being sent down. This seems to be a farfetched explanation.
Then, ⟪from ice⟫ can be understood in four ways. Three are the same as the above, and one is new.
Direction. ⟪Allah sends down from mountains in the sky from ice [in the sky]⟫. Maybe it refers to clouds being made of ice crystals.
Partiality. ⟪Allah sends down from mountains in the sky parts of ice [in the sky].⟫ This doesn't make sense.
Connection. ⟪Allah sends down from mountains in the sky ice⟫ where ice is the object being sent down. This makes sense and refers to hail.
Type for the mountains. ⟪Allah sends from mountains made of ice⟫. As for what ⟪from mountains⟫ means, that can be any of the above interpretations.
It's also possible for it to mean ⟪Allah sends down from mountains, in them is ice⟫. Here again what ⟪from mountains⟫ means depends on the above.
I could not find any report from the Salaf about this verse, except a report is attributed to Ibn Abbas (without a chain I could find) that he said: "There are mountains of ice in the sky." Seems to be made up based on someone's understanding of the verse.
Ibn Kathir notes that some grammarians say: مِن is preferably interpreted as direction, only then as partiality, and only then as type.
Based on that and what we covered above in terms of what interpretation is impossible, the best would be to say ⟪Allah sends down from sky, specifically from mountains in the sky, ice.⟫