breathable atmosphere included.
literally all thats required is 630 gigatons of nitrous oxide and the oxygen supersaturated ice crust (caused by billions of years of radiation bombardment) releases 0.3-3 bars of oxygen into the atmosphere.

dw we got a solution for the radiation too https://physicstoday.scitation.org/doi/abs/10.1063/1.2970203?journalCode=pto
VLF radio wave emitters could clear out Jupiters radiation belt to tolerable levels within 12 months.