Like people who own tons of Bitcoin or crypto but bought them without KYC? Either before KYC was a thing, or bought them through methods that did not involve KYC?
Usually whales are in a form of institution but if it's a single person, I think they buy bitcoin via OTC or over-the-counter. They find someone who sells bitcoin in their area then meet each other to do the trade.They don't go through to decentralized exchanges to buy because these DEXs' will definitely ask for some documents to withdraw that huge amount. It will also create a sudden pump on lower timeframes if they buy directly on those exchanges.
Coinbase and Binance offers that kind of service. Meaning if you want to buy let's say 10 billion dollars worth, you can't just end up buying it right up, it would make the market go super high in a single moment and you can't have a decent buy averages at all. So, what do they offer? You just put your money there, give an OTC order, and if there is another OTC order on the other side, it meets you and handles your deal and gets a good deal.
Because, there are sellers who would like to sell a lot without hurting the market, and buyers who would like to buy without hurting the market and they meet each other on these platforms with help. That way billions change hand, but the market doesn't move at all.