Crypto aside, I have idly wondered how/where the mega rich keep their money.

Is there a money manager effectively controlling a Schwab account with $1+ billion dollars? How do you minimize the blast radius to prevent internal/external loss of control? Even sub-dividing a fortune across N investment managers still leaves enormous targets painted on those accounts.

Or is it the more implicit threat that you do not steal from these people or the full weight of the government will aid in recovering these funds?

People who aren’t rich usually cannot understand how very little of it is typically liquid.

I sold some land, a guy sold me a Ferrari for it. I sold the Ferrari, never even saw it. He just couldn’t be bothered and wanted the land right then.

At that level you typically set up what's referred to as a "family office"

https://en.m.wikipedia.org/wiki/Family_office

The family office will manage the investment portfolio, typically across not only brokerages and banks but also direct investments / private equity/ vc / etc.