I don't have $200M in bitcoin, but just a couple of things need to be separated, there is no urgency like sky is falling end of the world to cash out $200M in 1 day, unless you thought it would crash any minute now to $0 in which case, how did you invest so much in something you did not believe in?
If I had $200M in bitcoin, I would contact several exchanges prior to transferring bitcoins to them and selling. There are OTC services as well, I'm sure you'd get champagne services from the likes of Gemini, Kraken, Circle, Fidelity, Bitstamp, etc, but they may question how you acquired so much so if your coins are dormant for 10 years on the original addresses, you won't have to prove much, since at that time, they were worth very little $ and they'll know that you're not involved in funny business like money laundering, if you paid $10,000 for $200M worth of bitcoins.
Personally, if I was him, I'd cash out 1000 bitcoins, and still hodl the rest, what would I need with $200M worth of fiat? then I'd have to invest it in a something like MSTR senior convertible notes who will give me sh*t interest and then spend the money to buy bitcoins or waste on company parties and yachts or some sh*t like that
There's no more fraud in bitcoin than in other cash investments as people are suggesting on this thread, there's plenty of liquidity for $200M in the market, you just gotta have that much legit bitcoins to begin with.