> Please, tell me what types of income earned by a U.S. expat isn't covered by a tax treaty?
I am not a tax person, but selling a house can cause you to owe tax in the US even if you did not owe any tax in the country you are living in (and sold the house in).
> Unlike the UK, the US levies capital gains tax on proceeds from the sale of a main residence.
I understand why it can feel unfair but by definition this is not "double taxing". The gains on the house were not taxed by the UK which is why he had to pay US taxes.
I am not a tax person, but selling a house can cause you to owe tax in the US even if you did not owe any tax in the country you are living in (and sold the house in).
Famously one of the reasons Boris Johnson tried to give up his US citizenship (https://www.bbc.com/news/uk-politics-30932891).