I believe every country has a reasonable threshold for a balanced account to avoid arousing suspicion from local financial regulatory bodies. Banks may inquire about your occupation and estimate your income, but if the assets disclosed exceed $10 million, I believe it would draw the attention of the IRS.
Gradual withdrawals are a simpler way to steer clear of scrutiny. If you're earning your money legitimately, I think you should be able to explain it well, and there shouldn't be any grounds for legal repercussions during an audit.
I don't care about the IRS knowing about my transaction. I can pay my taxes at the end of the year. I just want my transaction to go through and ultimately settle into my brokerage account(s).
Well, in that case one of the best option you can do is to get it OTCd in any banks that accepts bitcoin or any crypto exchange if you want to cash it out all at once, just to make sure your account is gonna be safe from being froze.
There's almost no way you can have it all cashed out using online transactions, or using the most basic trading in any exchange or any bank transfer for that huge amount of money.
IRS plus some transaction fees, I'm not sure how much is gonna be left after all those are taken out. So, you're not getting the whole $100m.