The US can default on (choose not to repay) its debt obligations.
The 14th does not override Congress' authority to tax and spend ... or not spend. Article I, Section 8.
What it hasn’t authorized is how the executive should raise the money Congress has told it to spend.
There is no limit on government borrowing besides the debt limit which comes very directly in conflict with the U.S. government’s constitutional mandate to pay its debts.
In nearly every other country the constitution would very clearly supersede the debt limit congress has created, but it’s not clear whether that’s a reliable heuristic in the U.S.
Only Congress can raise money through spending bills.
Ideally they are a paired activity, but issuing debt can be done with no corresponding spending. And spending can be done with no corresponding (exactly) debt or taxes.
And taxes are gathered by the executive, and the amount of taxes actually gathered is also independent of either body (as they’re a function of tax rules and executive effectiveness * economic activity, etc.).
[0] https://justinamash.substack.com/p/the-debt-ceiling-isnt-wha...
In theory, the US government would never go bankrupt as long as they can print more money. Which they always can, the dollar isn’t backed by gold anymore.