How many CEO's are there in the world?

Hundreds of thousands. Millions. I work for a small 35–40 person company. We have a CEO.

Any company larger than a mom-and-pop has some sort of CEO.

In the U.S. as far as I can tell the highest paid CEO of a publicly-traded company may be Elon Musk, who made over half billion $ in 2019, the most recent year I find info.
However, the top 25 hedge fund managers made $32 billion in 2020, well over a billion per person on average. The highest score was obtained by Israel “Izzy” Englander of Millennium Management, who got $3.8 billion for his trouble.

Lowest paid CEOs are probably heads of not-for-profit taking a token salary for legal purposes (e.g. being a paid employee let’s them enroll in the health plan).