Moving abroad attacks the retirement problem from the spending side rather than the saving side, and spending is the multiplied variable. Cutting annual spending by a third cuts the portfolio you need by a third.
The three things that decide whether it works are the residency visa and its income requirement, how healthcare is handled, and what the US still taxes you on after you leave.
Yes. The US taxes citizens on worldwide income regardless of where they live. Tax treaties and the foreign tax credit usually stop you being taxed twice on the same money, but the filing obligation does not go away, and neither do reporting requirements on foreign accounts.
Generally no. Medicare does not cover care outside the United States apart from a few narrow exceptions, so retiring abroad means buying local or international health insurance. In many countries that costs a fraction of a US marketplace plan, which is part of why the maths works.
In most countries, yes, and it can be paid into a foreign or a US bank account. There are a small number of countries where payments cannot be sent, so it is worth checking the specific destination rather than assuming.
It varies enormously and is usually stated as a monthly figure from a pension, Social Security or provable passive income. Some countries sit near $1,000 a month and others several times that, which often matters more to the decision than the cost of living itself.
Retire-abroad calculator
Enter what you've invested and a safe withdrawal rate. See how far that withdrawal stretches everywhere else — and where it covers more than your current lifestyle.