My insurance wouldn't let me back on if I quit, then when I got back to the states there was a slight concession and you could try medicare Advantage for a year, and were allowed back in if you changed your mind. Suspicious.

I'll link below a recent deep-dive into Medicare Advantage, if you care to view it. Otherwise, I can sum it up: flee. Don't do it. The name "Medicare" shouldn't even be associated with it. It's a private insurance program almost completely detached from actual Medicare. The low premiums are attractive, but you then have all the issues of "in network", and denials of coverage that any insurance has. And, if you do Advantage, you can almost never go back because a "Medi-gap" policy for standard Medicare can reject you for pre-existing conditions if you are moving from an Advantage plan to standard Medicare. If you don't do an Advantage plan, they cannot. So flee to pure Medicare with a Medi-gap, and count yourself lucky to avoid an Advantage plan.

On TMF, this topic came up occasionally. It was pretty universally stomped-on by the various board gurus every time.

YouTube: Medicare Advantage: Last Week Tonight with John Oliver (HBO) (LastWeekTonight)
(John Oliver)