They are different; ICJ is practically a fact finding body. The ICC, on the other hand, can issue warrants which obligate any signatory to seize the person into custody if they ever travel to that country. They have enough teeth in practice that even geopolitically important people like Putin will curtail their travel to avoid signatory countries, which is humiliating for the jet setting war criminal who is trying to pretend they are above the law and anyway they didn’t even do anything in the first place.