That's fair, though a lot of the wealth billionaires have is in their Net Worth, meaning it's the total value of all their assets, rather than just the money they have on hand. That's why when they say they're gonna pledge their wealth to charity after they die, which I know Bezos and Gates have both done, it doesn't really mean anything. The money they have is all in their company's stock, not in their pockets. Selling that stock to get the cash would mean relinquishing their control (and future payouts) of the company.

The exception to this is Musk, who buys out public companies entirely and privatizes them, making him the sole owner. But, much the same, his wealth is in the value of his companies.

They all obviously have an unimaginable amount on hand due to the payouts that come from owning billion/trillion dollar companies, but it's not like they each have 20 billion just sitting in the closet.