@brw, I even explored if the Millennium BCP Private Bank allows US investors, as one of the posters (who claimed to be from BCP) on the board suggested in the thread above. I connected over email with the private bank and the regular bank and they both confirmed that they do not support brokerage accounts for US customers. BiG or Bison are the only options for US citizens - non US folks have many more options including BCP. Someone did suggest that Banco Atlantico is also an option for US citizens, but I have not explored that fully to know either way.
Also, I have heard BiG also gives you a Multibanco card which is necessary if you plan to live in Portugal (though you can also have a separate bank account for that if you like), but I have heard it may be harder to work with them vs Bison. Which would be saying something as I have found things kind of slow already at Bison. More here…