In this video published August 31, pediatrician and medical school professor Dr Aaron Carroll points out that according to independent estimates, the Medicare for All program proposed by Senator Bernie Sanders would reduce total U.S. healthcare spending, in part because doctors and hospitals would be paid at Medicare rates.
Of course, healthcare providers have a fair amount of political clout and might lobby for higher compensation, which could end up wiping out the savings.
On the other hand, the current complicated system means that nearly a third of healthcare spending actually goes to administrative overhead that would almost certainly be lower in a single-payer system, so healthcare providers might well wind up better off even with lower gross billings.
It's of course worth recalling that all other advanced countries spend less per citizen, often a lot less, than the United States does, and our healthcare outcomes aren't on the whole better than average. Single-payer systems, as used in the United Kingdom, Italy, Canada, and Taiwan, but the better-regulated multi-payer systems found in Switzerland, Germany, Israel, Japan, and elsewhere still cost less than ours.