Large BTC buy in - Best Method

Hi all, looking to understand what is the best way to make a large purchase of BTC - not DCA etc but just one single purchase.

Let’s say hypothetically I wanted to buy $10mil+ worth of BTC, what’s the best way?

When I have bought I’ve always used Binance/Coinbase, and then transferred to a hardware wallet, but it’s only ever been fractions of a BTC.