The way a country does this while technically still honoring its obligations is to allow steep inflation, i.e. print money like there is no tomorrow. That way it gets to pay its loans back with much cheaper money.
Beat me; Globama will print more money and tell the sheeple that the problem has been fixed.
Which is what virtually every country did back in the 1970s.
Much of the debt is short term debt and hence can’t be rolled over unless long term interest rates are low. Long term interest rates will be high if there is a substantial risk of currency devaluation or outright default.