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.
Yes, excessive money printing will cause inflation to soar but its burden is not on the government but on the ordinary people. Actually, this is what all governments do when they face things like an all-out war. They start financing their expenses through money printing as this is a sort of last-ditch recourse. The Zimbabwean government just lost touch with reality. Most other governments know better and use the inflation tax wisely as it is pretty much like the law of diminishing returns until the returns turns into real problems