It doesn’t work the way you think it works.

When they say people are worth x billions they don’t mean their bank account. It’s more like “Wall Street says Tesla is worth X today and Elon owns Y% of Tesla”.

If he actually tried to sell any substantial amount of the stock the price would plummet due to insufficient demand and he wouldn’t be worth much anymore. It’s just a market valuation, not actual money that could be accessed.

Additionally - there would still be zero extra dollars going to your schools because no one would make a cent of income past 999 million if they weren’t going to get paid for it. Elon would just go on vacation instead of working 100 hours a week.

Probably best to spend some time educating yourself about economics, markets and finances rather than throwing out ideas that would make sense only to toddlers.