I’m pretty sure most of this is also what, say, EU has to deal with. They most certainly have bureaucracy, unpaid bills, 24/7/365 services, complex diasnosises…

Some big differences: Without the equivalent of AMA lobbying Europe has a lot more primary care doctors per capita than the US. No long history of trying to get everyone healthcare without using taxation resulting in a pile of Rude Goldberg regulations that nobody understands. Regular use of cost-benefit analysis in deciding what procedures or drugs to pay for, now that the FDA has approved aducanumab it's going to be available to people even though it probably doesn't work and is breathtakingly expensive.

Single payer largely avoids unpaid bills and a great deal of bureaucracy around billing. This is true even in the US, just look at the VA’s costs. The VA is serving a very expensive population and it does so relatively cheaply for the US. At least in terms of services rendered rather than just per person.

The 24/7 comment was in comparison to dentistry. It’s tempting to compare getting stitches to getting a filling but inherent overheads are associated with an ER which must be added to the bill.