Actually, for most of the matter in the Universe, about the only thing we know for sure about it is that it can’t exist in a plasma state. It’s only the small portion of matter that we have a clue about that’s mostly plasma.
If you’re talking about dark matter, I figured we know little enough about its properties that I just took it off the table. If you want more precision, most of the normal matter in the universe exists in a plasma state.
Isn’t the sun almost entirely supercritical fluid?
In any case a good line between ongoing reaction and explosion would be that in an explosion the rate of reaction escalates, often exponentially, until the reactants are depleted. In an ongoing reaction the rate is about the same for the early reaction products as it is for the late ones.
In the sun, a typical hydrogen atom takes billions of years to get pushed into fusing. So, the sun is a reactor, not a bomb.