it's a tax on billionaires.  Here's a decent Forbes article with some good examples of a how it would apply to a billionaire who happened to use the unrealized gains in their electric car company to purchase a social media company.  https://www.forbes.com/sites/andrewleahey/2024/04/30/unrealized-gain-tax-a-coming-sea-change-in-fy2025-budget-proposal/