What any whale should be concerned about is the legitimacy of that BTC, if it's not bought/arranged through illegal means, then it's a go. It's, however, not uncommon that banks flag accounts, but it would be for a little while if you have all your proofs provided to them, it's as simple as that.

While some that would want to receive a very huge amount could notify their banks earlier and provide proof to avoid delay. It's all business for banks, they are only being careful of what to tell regulators, and if you are detailed, it's no issue for them.

I will like to pretend as if this happened to me, I don't normally leave a large amount of money in my bank account and I use a private bank not the public banks that belongs to the government, I can change over 20,000$ to my native Fiat currency and I don't see anything wrong in doing so, the only time to expect problem is if the bank figure out that you are into crypto investment while there is a ban on crypto in the country.

Even if I have a very large amount of money in Bitcoin, I won't be stupid enough to convert the whole money into Fiat and send them into my bank account, my money is safer in BTC or USDT than my bank anyway.

Why would anyone do that? To show off? If you want to build a house you can't build it in a day, so take your time to use a certain amount to continue the house project every month, what could you possibly need the large amount of money for if you convert every thing into Fiat? It makes not sense.

I was thinking that this could be frustrating perhaps for someone who is super happy to find his private keys after so many years and who thinks that he has more than enough to buy a house but finds himself a little stuck because he cannot not buy his house in BTC or repatriate his funds to buy one.

There are some banks that accept bitcoins directly by accepting bitcoins they give fiats money to customers but not all countries have such banking services. There are some countries where the banks of the countries are far from accepting bitcoins and there are various negative comments about bitcoins, then how do the people of those countries convert huge amount of btc into fiats money. In this case, people from all those countries can use the P2P system of different exchanges or convert their BTCs into fiats by buying and selling with different members.

Ownership can be proved in a very simple way, and that is by signing a message with one or more public BTC addresses. After that, he has to find out the process of paying capital gains tax, and then he can sell his BTC without any problems.

If I found 10 BTC and wanted to sell them all I would have to do is submit a tax return and explain when and in what way I acquired that BTC, and for all crypto assets acquired before 2016 I do not pay any tax (local law). I don't think this kind of thing is a problem, at least not in countries where BTC is not declared illegal or if it is not acquired illegally.

Walk to an offline broker and negotiate a deal with them. Receive a portion in cash and rest in bank. But it is wise to not convert a huge amount of bitcoins at once. If you suddenly receive a huge sum of money in your bank account which doesn't match the previous transaction trend, your bank can freeze the account.

So always convert a little amount of money which doesn't raise suspicion. Or do cash trade with offline brokers.

After reading the first page of replies i can conclude that it is not possible for an ordinary person who just became a millionaire to withdraw money by keeping his/her identity hidden. As, i have read recently that there are exchanges that do not require KYC and there are people who gave 100% importance to remaining hidden of course their intentions are not bad always. Just like our respected Ratimov.

The point is, if you are a guy who gives hundred percent importance to anonymity then it will become die-hard for you to withdraw all of your million in one go on any centralized exchange. As divide and conquer rule best suits you here but you needed them in a hurry so what you can do is maybe contact any group of people who would withdraw your money using their centralized exchanges into their banks and then they would send it to you, maybe you could ask your friends or relatives to make this happen for you but still, it will be opened to everyone. (no secret will remain hidden).

I would suggest, trying to negotiate with the seller of the house, maybe he would agree to receive direct BTC so you could just hand over your BTC or Wallet containing BTC to him. Everyone has there own way to deal with things and find loopholes and different ways based on the country you are living, so answer will never be same and many will hesitate to share this info too.

It won't be a problem if the bitcoins are his because the government has nothing against him as long as the bitcoins are yours. But the problem here is the envy you will face because once there are people who know about the massive amount of bitcoins you have, most of them will be interested in getting it from you, and you won't get away with it once they know your location. That's why the best thing to do is to lay low and chill, and you just need to learn the basics on how to hide your identity when converting it to fiat to protect yourself from those kinds of guys and also from huge numbers of questions from the banks.

I think it would be best to ask a whale if he know someone and ask how a whale would convert his BTC to fiat money. My guess on how they withdraw their money is to never withdraw a huge sum of money instead withdraw portion by portion so that it won't noticed. That's what some people in my country did when they have earn money from crypto and you say that the amount is in millions in fiat moi.