The core of MMT’s story is that money creation begins and ends with government spending and taxes respectively. Beyond that I am unsure as to how much their theory differs from mainstream economic theory.

At the end of the day they seem very much rooted in the question of wether there are productive economic assets that can be utilized. Yes => the government should spend money to use them, don’t worry about deficits, No => either spend less (create less demand for resources) or tax more (remove demand from somewhere else). In the end, there’s no reason assets should be left to no productive use, by their estimation.