I recommend Stephanie Kelton's "The Deficit Myth" for more background on MMT: https://www.amazon.com/Deficit-Myth-Monetary-Peoples-Economy...
The point of that woman is simply: let the deficit go up ad infinitum (in USD value), it doesn't matter because as the central bank keeps printing money, the value of the deficit actually goes down (because the USD value goes down), so the value of the deficit is stable even if we don't perceive it to be this way. Quite BS imo
Reserve currency status does afford increased deficit-spending capacity. But it isn’t an immutable, environmental variable. Deficits and reserve currency status interact. If a country runs up large deficits in the name of its reserve currency it affects others’ inclinations to hold the currency in reserve.
Precisely where this happens is difficult to predict. It involves many levels of animal instincts. That it happens, however, is well evidenced.
By analogy: we know the plane will safely travel at a 300 flight level. There is theoretical work for higher FLs. Do you point up the nose of a fully-loaded plane until the wings or engine or fuselage fail?
Piloting federal fiscal policy on MMT is akin to steering the plane to FL 100 and keeping an eye out for a stall. You might get lucky. But you should have experimented in smaller and more-controlled settings first.