I don't think it's a good idea for you to sell your bitcoins at once when you have a huge amount of it and the best thing you can do about it is to diversify it whenever you want to convert them to fiat by using multiple exchanges and cash them out in each one of them.
If these centralized exchanges are all KYC mandatory, it's not big different if you cash out from one centralized exchange or from multiple centralized exchanges. They all know who you are by your KYC documents submitted for verification.
the best thing to convert it is using P2P in some known exchanges which most people do nowadays.
The most common P2P exchanges are like a most favorite targets for banks and governments to put these platforms under their radars.
P2P can be traded through a P2P platforms that increase risk for your privacy.
P2P can be traded in person, it's good for privacy because you will complete your trade in cash, in person but it has another risk. You can be robbed, physical attack or you can receive faked cash.