Medicare A and B pay nothing abroad.
Some Medigap plans will pay Emergency Only during first 60 days of travel outside US, with substantial deductibles and limitations, and by reimbursement only.
Advantage plans will pay Emergency Only but you cannot belong to an Advantage plan if you do not live in US for at least six months each year.
This article explains it well. https://www.pbs.org/newshour/economy/retiring-abroad-what-medicare-plan-should-i-get
"Medicare generally does not cover medical expenses outside the U.S.
First off, Medicare generally does not cover medical expenses outside the U.S. There are limited exceptions for people living near the Canadian or Mexican borders. Medicare may cover them for emergency care if they can document that going to a non-U.S. care facility was a medically appropriate decision. There also are some situations where Medicare will provide coverage to someone on a cruise ship near U.S. waters.
People with Original Medicare, Parts A and B can get a Medigap policy (also known as a Medicare supplement plan) that provides coverage of emergency medical expenses outside the U.S. Medigap plans are regulated and sold at the state level. According to UnitedHealthcare spokeswoman Sarah Bearce, you need to be a resident of a state when you first buy a Medigap plan. After that, if you moved outside the U.S., your Medigap plan would continue in effect so long as you paid the premiums.
However, she notes, only Medigap plans C, D, F, G, M and N have foreign travel coverage, and there are restrictions: “The foreign travel benefit covers 80 percent of ‘foreign emergency care that begins during the first 60 days of a trip period’ after a $250 annual deductible, and it has a $50,000 lifetime maximum. This benefit likely wouldn’t be useful if you permanently live outside the U.S.”
Medicare Advantage plans are more restrictive. “To be eligible for a Medicare Advantage plan,” Bearce says, “your permanent address, as on file with Social Security, must be in the plan’s service area. If you signed up for a Medicare Advantage plan while in the U.S. but then relocated overseas, the plan would be required to disenroll you after you were out of the plan service area for six months.”