The source of our rising debt is a built-in and growing imbalance between taxes and spending. [Source]
No, it's not.
The source of our rising debt is borrowing. Stop borrowing, and there will be no rising debt.
Create enough new currency and use it to pay off the national debt, and there will not only be no rising debt, there will be no debt at all. There will be no interest payments on the debt because there will be no debt in the first place. There will be no taxes to collect to pay any interest for the same reason.
Where's the money going to come from to pay for Medicare for all? Create new money to pay for it.
Healthcare is part of our GDP. If the demand for services, equipment, and drugs goes up because of single-payer, then match the demand with a proportionate increase in the currency spent right into the healthcare system: Medicare. All that will have happened is a larger GDP, not inflated healthcare prices and not reduced goods or services.
The only constraints would be training the people, building the facilities, and supplying the manufacturers with resources (raw materials). We're already doing that and can get much better at it if we put our minds to it. The same applies to everything we want and need in the form of the Green New Deal.
We certainly can't do worse than we already are.