So we are only talking US stocks here.
There is no withholding tax on the sale of US stocks, even if there is no tax treaty. There is only withholding tax on dividends.
But isn’t that ALWAYS the case, no matter where your broker is located? That only depends on your personal tax residency, right?
And for ETFs, it depends on where they are domiciled. And you should be able to buy Ireland-domiciled ETFs through IB HK? For Ireland-domiciled ETFs, there is only a 15% withholding tax.