If a BTC portfolio gains millions of dollars, is it really that easy to just sell them on the exchange? They just let you deposit millions into your bank account? Or what do you do when you want to cash out?
I think, it will require you KYC before you can withdraw that amount, and I do not recommend to save 1m usd in a certain crypto exchange, better to use hardware wallet for better security, it will make you feel safe rather than in exchanges, no offense but few exchanges has already experienced attacks from hackers, yes your funds are safe but it is much better not to feel anxious because of that, or you may diversify your money into different exchanges.