Government debt isn’t “debt” in the classical sense. Let me suggest an analogy: a bank lends you a loan at intrest, but no expiry date. You can pay back the loan at any point in the future. Not only that, the bank has no ways of enforcing you to pay it back through legal action. On top of that, you are infinitely credit worthy, you can get as much loans as you want, including loans to cover existing loans. Would you consider this a “debt”. The answer is that it’s nothing like a debt in any meaningful sense of the term, it is merely a label used because of accounting convention.

Could you “print”* an amount of money several times the world GDP and get inflation?

That depends whether te money is circulated at all. Inflation is not a function of the money stock, it happens when sellers collectively mark up their price above current market rate. This is easier to do with rising expectations of higher return. The money stock is not some magical denominator on top of a real goods numerator.

*(it’s really just incrementing a number in a database, zero production cost, so print is another misnomer)

Forget the currency aspect, which is nothing but a distraction. What matters is the balance between production and consumption. Without debt one must first produce goods before one can consume. Individuals can get around this by taking out loans, borrowing the opportunity for consumption in the present from someone else with a positive balance. For society as a whole, however, there is no avoiding it: goods which have not yet been produced by someone are not available to be consumed. Introducing new currency in order to fund consumption disrupts the balance, since there is no production to offset the consumption. The result is that society becomes poorer; capital is consumed without replacement, productivity falls, and goods become less affordable. (By this I refer not not only to rising prices, but to prices rising faster than wages, a increase in the cost of goods even after adjusting for the change in money supply.)

> Inflation is not a function of the money stock, it happens when sellers collectively mark up their price above current market rate.

The term "inflation" has multiple definitions. Yours is popular in political circles but is not very useful as an economic indicator because it conflates ordinary changes in prices due to supply and demand of goods and available production capacity with changes due to shifts in the money supply. The general increase in prices which results from consumption of capital is nothing like the change in prices which accompanies a deliberate increase in the supply of money. The former is a useful economic indicator which suggests a need for more saving and prudent investment, while the latter offers nothing but noise and tends to encourage malinvestment and waste.

No . But you are getting there. Yes fiscal policy is the lever that determines the amount ( quantity) of money ( or demand ) driving the economy . Monetary policy is interest rates or the price of money. And ,there is mounting evidence that hight interest rates actually have the opposite of the intended effect . That is, that higher interest rates lead to higher net income to the private sector which is a bit inflationary.

> higher interest rates lead to higher net income to the private sector which is a bit inflationary.

There a paper for this? low interest rates tend to be associated with poor economic conditions, in the extreme liquidity trap or secular stagnation, so this conclusion makes sense though the causal effect is the opposite of what is suggested by your comment... As an example, interest rates (ex fed funds) were really low during the great depression!