Counting:
Heads of State and Government, regardless of the title; Governors-General and other folks that represent a Head of State that lives abroad; and individual members of dual/collective heads of state/government.
Is this only for heads of state? What about heads of government (e.g. Prime Ministers)? Governors-General of Commonwealth Realms, who are sorta-kinda heads of state?
If this is only for heads of state, King Charles is currently the head of state of Canada, Australia and NZ, so the probabilities should likely be more similar to each other.
@strutheo the rule of thumb is: the Head of Government is the person with the actual political power, and the Head of State is a figurehead. A Prime Minister is almost invariably Head of Government. Monarchs are always, and Presidents are almost always, Heads of State (even if they have power, like in Saudi Arabia). So in countries where there is no monarch and no Prime Minister, only the President like in America, they are the Head of State and of Government all at once, a twofer.
And since King Charles can only live in one place, the other countries (Canada, Australia, New Zealand, Papua New Guinea and so on) where he is King have representatives, the Governors-General.
In my opinion, this question should count: Heads of State and Government, regardless of the title; Governors-General and other folks that represent a Head of State that lives abroad; and individual members of dual/collective heads of state/government.