Selling a few million dollars worth of bitcoin would only slip the market a couple of dollars if at all. Go look at bitmex or bitfinex's order books - they have plenty of liquidity.
95% of that volume is fake [1] especially on bitfinex haha, they’re the scammiest. When they launched they were just importing order books from other exchanges to make it look like they had volume, and they launched Tether when they lost banking which also lost banking and had hundreds of millions seized for money laundering. Bitfinex is the biggest scam in the space and that’s saying a lot.
[1] https://www.forbes.com/sites/cbovaird/2019/03/22/95-of-repor...