Congress has the power to “To borrow Money on the credit of the United States”. That’s Article 1 of the US Constitution. They need to explicitly authorize borrowing money. Only Congress has the authority to “To lay and collect Taxes, Duties, Imposts and Excises”

A spending bill that Congress passes does not “implicitly” authorize borrowing money to pay for it, anymore than it “implicitly” authorizes raising taxes to pay for it.

Historically, the executive branch appears to have obeyed all these statutory limits. One possible exception occurred in 1789, when Alexander Hamilton obtained loans on his own authority to "meet expenses incurred at the beginning of the present government of the United States." But Hamilton conceded the next year that the loan was "the result of necessity," and told Congress it wouldn't happen again.

In a 1930 annual report on the state of American finances, Treasury Secretary Andrew Mellon wrote with recommendations for a single statutory debt limit, separate from individual appropriations, which would make Treasury's life easier.

Congress acceded to Mellon's request. By 1941, Congress had combined all the statutory borrowing authorities and limits into the single cap that persists today.

(Excerpts drawn mostly from this blog post: https://reason.com/volokh/2023/05/24/why-do-we-have-a-debt-limit/?comments=true#comments)