1. No American will ever be Secretary-General of the UN. It is an unwritten rule that no country with a veto on the Security Council may have one of its representatives serve as Secretay General.
2. Being Secretary-General actually involves work -- occasionally -- and his staff is insignificant compared to the staff of POTUS. Obama is lazy and disinclined to work. He is more inclined to lie on the beach in Hawaii. <
Consequently, he will pursue the latter line of work after he leaves office.
I wouldn’t put it past him to represent some country other than ours. He has no loyalty but that to himself.
As for the work part of the job, heck, he’s played his way through the presidency for the most part. He’s gotten more experienced at being a slacker.
I don’t put anything past him.
But having said that, you may well be right about him just wanting to lay around on the beach.