This is not true. Government spending is not “paid for” by taxes. Spending comes first and currency is then taxed back and ‘destroyed’. There is also no reason the government needs to issue debt in the form of bonds, etc. That’s a policy decision and not a necessity. It’s an imposed constraint.
The only ‘real’ constraints on government spending are its effects on inflation and unemployment which is why those are relevant considerations for Medicare for all. If single payer turns out to be deflationary, then we ought to cut a tax like the payroll tax. If inflationary, we ought to look at increasing taxes somewhere else.
I’m actually not sure if the effect will be substantial in either direction but we won’t know until it takes effect.