To clarify, Elon musk has had years where his net worth increased by around $121B (such as 2020 and 2021, a time when a lot of people were suffering) but he did not pay income on this increase because an overwhelming majority of it was not reported as income.
If Elon Musk were paying regular income tax on this increase in net worth, he would be in the top bracket paying 37%, which would be about $44.4 billion. Instead, he's paying about 1/4th that. Why? Because he's able to benefit from loopholes and legal tax avoidance schemes, such as borrowing at a very low rate against unrealized capital gains, that most taxpayers are not able to benefit from.
A large part of why there is such a massive disparity in wealth between the rich and poor in our society is that we allow people who already have a ton of wealth to concentrate wealth very easily while avoiding tax, like this. Closing these loopholes is important to ensuring equality of opportunity and also avoiding the extreme concentration of power in the hands of a tiny number of people.
And we see the negative effect on the world of allowing Elon Musk to have such wealth and thus power.
Please, support closing these tax loopholes. At a bare minimum I want him to pay some sort of base level of tax on the increase in his net worth. But I also would prefer that the top tax bracket was much higher. 37% is much lower than it was historically. Not that long ago it was even as high as 90%. Having it that high is a strong disincentive or deterrent to people getting the sort of compensation that leads to people becoming super wealthy. But it's probably more important to fix the loopholes because if you just raise the rate but still allow legal tax avoidance, people will just avoid paying tax.