No there isn't. The text of the Constitution says the opposite: it makes appropriation a necessary condition for expenditures, but omits any clause making it a sufficient one. And the only case law on this issue is Train v. New York, which assiduously avoids ruling on the separation of powers issue. So there is neither any basis in the Constitution itself nor any basis in case law for your contention.
The Founders had just fought a war over unjust taxation to support the head of state's pet projects. Thus they required all funds to be appropriated by Congress. But it is still the head of state that actually spends them. The Treasury has always been part of the Executive branch, ever since Alexander Hamilton led the Treasury under George Washington.
Our country is built on checks and balances. The Executive controls the Treasury and spends money out of it, but is checked by the Congress, because the Executive cannot spend money without it first being appropriated.
I know recent history makes it hard to imagine a successful impeachment+conviction when both chambers are controlled by the president's party, but that doesn't change anything; there is literally no other legal path to reigning in an authoritative executive, especially with the 2024 presidential immunity ruling. Party bonds are strong, but at a certain point, even the most loyal congressperson will start to resent being made into a rubber-stamp like the legislatures of Russia & Hungary have been.
B) I really don't think the global scene backs up the idea that truth isn't effective -- there's lots of complex things going on, and some amount of emotional propaganda is always necessary, but we should never abandon the truth. Regardless of how effective it is in the short term, basing a political project on lies means it has no core, and can end up corrupted/way off track in short order.