It would be a bureaucratic pain but if I were to move back to Europe (having become a US citizen) I don’t expect I would end up paying any tax to the US after a

It would be a bureaucratic pain but if I were to move back to Europe (having become a US citizen) I don’t expect I would end up paying any tax to the US after applying the foreign tax credit. But there could be a whole lot of complexity around stuff like ETFs and mutual funds and whether they were recognized by both countries.