I don’t think you are eligible for diplomatic immunity if you are a citizen. He might choose not to extradite himself but he plans a visit in 2024.
I think he either voted for Sérgio Massa, whom he supported publicly, or symbolically cast a blank ballot. The other options are to declare that he was ill or 500 km from the nearest polling place, or pay a 50-500 peso fine. None of these are off-limits for somebody with a good diplomatic position and a large amount of staff.