As this Minsky guy said, everyone can create money
But apart from everyone else, the central authority (otherwise known as government) can also force their money into acceptance by the local populace. That technically means they have a sufficient leeway in how much they can print and that basically answers your question. The government can fund their expenditures by simple money-printing (it is called an inflation tax, for the inquiring minds). Indeed, there are limits to this effort but any government at some point had been doing exactly that in the past, and there is no reason to believe that they won't in the future. Such is life and then they start the printing press
Govt currency acceptance is easily done. People need to pay a lot of money to govt, so, it has acceptance. People are forced to accept it. However, there's some exception as well. Look at Zimbabwe. Because of the inflation, govt decide to introduce new currency which also face the same. They weren't accepted by the people.
Govt can't print money if they need to fund expenditure. Money printing can affect the economy widely. For ex, if govt print more money than M0 (I'm not certain what's the denomination), economy will face a significant inflation.