If Bitcoin only backs assets, then it can't exceed, or even approach the total value of world wealth, currently $454T
At $21M for 21M coins, this approaches world wealth.
If Bitcoin is used to back debt, then you can add a further $315T of value, so if we assume $100T of asset value + $300T of debt value, then we approach $21M
However, I'm not certain Bitcoin can survive being used to back debt.
Gold never did that.