Tax the income of corporations not the profit. The same way you get taxed your VAT. That means that corporations can’t tax evade: if they make income in a country, they get taxed. They can’t go an declare the profit in the Netherlands or Ireland and skip paying taxes.
Create and use parallel institutions to allow society to thrive without needing to play the billionares economy game. Example: communication tools outside of a market involvement such as Lemmy, Element (matrix). Economy tools. Association tools. See the application of Dual Power by socialists, which is what you are proposing here, a redistribution of power and wealth.
You perfectly can sell GPL code. And you can double-license yourself (provided that you are the copyright holder) as GPL and a privative license. A lot of companies do that, legally and correctly.