Basically if you live in an expansion state you're eligible if you make less than 128% of the poverty level. Which is about $16,000 a year for a single adult. If you don't live in an expansion state your mileage may vary. There was a buffer during the covid emergency stage where states were a little more generous like Texas than they would otherwise have been.
But Texas in particular at one point kicked you off Medicaid if you made even like 6K a year. They were only supporting people that made less than 25% of the FPL. Certainly not 128%. I think all but 16 states at least now extend to that
There's a few public hospitals and there is a law that mandates if you show up in emergency room they have to provide you with emergency care, although they can bill you for it. Medical debt is the leading cause of bankruptcy in the United States. It's basically not existent in the rest of the industrial planet. And even then it's just emergency care, doesn't cover follow-ups, doesn't cover any referrals.. but that is essentially the insurer of last resort is an emergency room.
People that make less than 128% of the poverty level are eligible for Medicaid. Some people are stuck trying to stay below the poverty level literally so they don't lose their health care. In United States you're better off making 16K a year if you have serious health expenses then you would be making 25k a year.
People over 65 are eligible for Medicare. Everyone else has either no insurance or employee based insurance which is terrible for obvious reasons. That jobs are incredibly temporary. It also is a huge point of leverage for workers that want better conditions but can't afford to quit or they could lose their health care.
But yes it is very lame and peculiar that the United States is basically the only major industrialized nation that doesn't have some kind of centralized universal health care plan where everyone is automatically opted in.
It's disgusting, and it's also grossly inefficient with a third of our cost going to paperwork and we spend 20% of our GDMP on health care when the average OECD nation spends about 10% and covers everybody.