the free energy framework provides a really natural explanation for what suffering is. "good" vs "bad" feels like such a basic quality of subjective experience, but neuroscience says the material correlate is dopamine or opioidergic neuron firing or whatever. that doesn't make sense, it's way too arbitrary. in the active inference framework, suffering is exactly free energy. it's the same principle for any system. to the extent that the system is trying to assert that "it is the universe", and the rest of the universe is shooting that theory down, that's the subjective quality of suffering.
of course, the concept of a "system" is just something we lay down post hoc to try to understand. you can draw a boundary anywhere you want and call the inside a "system" (although this might get increasingly pointless for weird boundaries). and then our concept of "suffering" would match up with the free energy of that "system".
this is a nice explanation for what happens in addiction, i think. when you look at the system-boundary around your relatively shallow ego, free energy actually decreases when you take drugs (or do whatever addictive behavior), because the drugs help this shallow system to live in a more isolated dream, where it's not exposed to the truth of the rest of the world which it's denying. but simultaneously, if you look at the system-boundary around some deeper identity of the individual, the drugs are making things worse -- creating more suffering. so at the same moment, there's either more or less suffering depending on what system-boundary you're considering.