The neural pathways guiding positive affect may atrophy significantly during a prolonged depressive episode, and there is no instinctive restart mechanism which builds up these pathways again once the episode is over. It is similar to people whose body atrophies significantly after a injury and require PT in order to regain control of their body. As a general rule, once something which is naturally self-sustaining atrophies beyond a certain point, its feedback loop can no longer generate the upward momentum required to sustain itself, so it effectively turns off.

There is a sort of simple solution though, which is to re-stimulate the pathways manually so as to jumpstart the feedback loop. This requires a sustained effort, becoming effectively an exercise, in a context in which you most likely have no idea what to do or how to activate those pathways. So there are two components at play - 1: You must repeatedly active the pathways day after day for potentially weeks to months to years (depending on skillfulness and time committed). 2: You must know how to activate the pathways. Being the case that these systems are by their nature self-sustaining, that being they operate without any necessary conscious awareness, we generally do not know how to actually do what we do even when the pathways are healthy. In that way they were only learned implicitly, so there is no knowledge of how to jumpstart the pathways.

All that is to say that blunted affect seems quite natural of a response given the nature of the system. The solutions then require either the external world to active those pathways for you (TMS, support system, drugs, etc), or you yourself must find the capacity to generate the effort and activate the pathways, probably with direction as to how to active those pathways since it is not implicitly known.

This is why Positive Affect Treatment appears to be one of the better therapeutic treatments for anhedonia, as the exercises require one to manually flex the affective muscle (which is essentially just your imagination), even though it will not feel like they are doing anything valueable at first and they will most likely hate it and want to stop.

This is why one must first understand the nature of how learning works so that they can clearly see how the onset of learning is always a confusing walk in an unknown space with no immediate tangible results. They must also understand how learning works through repeated neural activation over time, and see this clearly as fact. They must understand how entering with a beginners mind, clear of judgments and expectations, will produce results the most effective results as it A. does not encode the negative emotions one might otherwise generate in the act, and B. encourages initial random walks of the learning space early on which as machine learning proves to us is necessary to escape local minmas (i'm suggesting beginners mind is like a high learning rate). It also requires something of a leap of faith, even if you understand all that and see it to be true, as until you have undergone the process yourself, you will not know for a while whether it actually is true, and the skepticism will gnaw at you, especially since the natural anhedonic draw is into low effort and low motivation.

The most difficult aspect of it all is ultimately that you have to rest in a place of both knowing and not-knowing. What I mean is that that is what the experience is like, for imagination is an act of knowing, but you are knowing something that you have no knowledge off, so an act of knowing what is not-known, which is frustrating. I recommend doing this in bed at night when the imagination is often at its most active and immersive, and you will likely find it entering into your dreams, which will repeat the patterns some time over. I don't think one needs PAT specifically, but it does provide some ideas, and one might best tailor it to their own self and what they feel like doing and would enjoy the most, which will make it more sustainable over time.

I say all this as this is what I did and it worked for me and the general anhedonia research supports these claims which is why I did it.