In absolute terms, the US is probably competitive as the most indebted entity in history. In relative terms, they are well past the threshold where countries pay back their debts in full. Their past performance isn't really a guide to what happens next, unless they've changed what is being measured the US is a financial basket case [0]. They aren't going to pay back what was lent to them in real terms, the idea is preposterous.
https://carnegieendowment.org/chinafinancialmarkets/86397 presents a reasonable argument for why you can't just compare debt-to-GDP between very different systems and expect it to make sense. (The US in particular is, of course, in many ways an outlier.)
[0] https://www.longtermtrends.net/us-debt-to-gdp/