I guess it's not a problem for someone famous, but for an ordinary citizen, how it happens if he lives modestly, recovers his private keys that he lost 10 years ago and finds himself with millions?
If Bitcoin is illegal in your country then there might be a problem and Bank can detect suspicious activity. So the best option to send it to a trusted centralized exchange and convert it to stable coins. If you need fiat then just trade with P2P option.
And I don't think an Ordinary citizen need all of his million dollars at a single time. He can secure his funds by buying stable coins and storing in a non custodial wallet. Then he can follow this P2P procedure again and again to convert it to fiat.