Well, not really. He can't actually spend that money. When he bought twitter, he had to take a bunch of sketchy loans and some of his stocks dropped because he had to sell a lot.
If he actually sells a bunch of his stocks, the price will dip and make the rest worth far less. So it's not actually spendable money.
It's more of a power measurement. If you have a billion you have influence over that many assets.
Also a problem with wealth tax. If you have to sell assets to pay it, that could have a bunch of weird effects. I think Denmark doesn't actually tax your assets, they just increase your income tax if your wealth is above a certain level. But I'm not 100% on that.