alt Hacker NewsTotal debt / GDP is the wrong metric for that. There's no limit to the serviceability of debt in a currency you print.
It makes more sense to conceptualise it as the total size of a giant savings account run by the government.
We are walking further out on the ice but that is measured more in other ways - with harder metrics like inflation, access to cheap energy, resources, industrial density and capabilities and access to technology - not this headline number.
Even if we just ignore inflation and other issues, there's still a hard limit because governments don't literally just print money, but sells bonds at market rates. As confidence in the economic stability declines the interest rates the government is required to offer on those bonds trends upward. So right now even 10 year treasuries are selling with just under 5% interest. As a result we're now paying $1.4 trillion per year in interest alone, and that number is going up far faster than the economy is growing. This [1] graph looks quite disconcerting. And it's a vicious cycle. The less confidence there is in the stability of this game, the more the government will have to pay to sell that debt. And the more they have to pay, the more debt they end up needing.
[1] - https://fred.stlouisfed.org/series/A180RC1A027NBEA