It is odd to keep repeating the point that Musk’s money isn’t held in cash or sitting in a vault, as if that somehow makes it less real. It would be bizarre to keep more than a very tiny percentage of wealth in cash, to get eaten away by inflation. Wealth is held in income generating/appreciating assets, that is what keeps it growing.
In a personal sense there is nothing on earth that Musk could choose to buy that would cost more that the tiniest percentage of his wealth. Gigayachts are the most expensive things humans have come up with so far as a thing to spend personal money on, far more expensive than houses or jets, but even they have a limit.
If a billionaire/trillionaire wants to spend a huge amount of money on something, they don’t have to sell assets to do it. They use arrangements like Securities based Lines of Credit, where some of their stock is put up as collateral against a loan. Loans aren’t considered income, so they get access to a vast sum they can use to fund their lifestyle and make more acquisitions, but none of that money is taxed (and because they don’t have to sell their stock to do this, there is no capital gains tax to pay either).
These loans are considered low risk, so the rate of interest will be very low. In the meantime their wealth grows at a pace that far outstrips that interest. They never even need to pay the debt, they can just keep refinancing it until they die, swanning through life without having to pay tax.
What this vast hoard of wealth does (apart from allowing them to buy up assets that create yet more wealth) is buy influence and power. It is no coincidence that Trump surrounds himself with billionaires, or that Musk bought Twitter as his personal megaphone, and found himself in a position of genuine influence within the US government.
Does anyone think that these incalculable sums of money, concentrated in the hands of so few people, will to lead to less corruption in the world? The US has already demonstrated how quickly a democracy can bend towards oligarchy - a regime now run by the mega-wealthy to serve the interests of the mega-wealthy.