I can relate to this because I have dysthymia, which is a kind of chronic joylessness. I think this is an often overlooked aspect of depression. And it's often overlooked in treatment too. Because joylessness is not a crisis in and of itself. And treatment often tends to focus on acute symptoms. Whereas dysthymia - and I'm guessing anhedonia too - is chronic (long-term).
I wish I had some answers. Treatment-resistant anything is really tough. And treatment-resistant depression/dysthymia/anhedonia seems to receive very little attention. On the outside, my life looks great. There is very little "wrong" with my external situation, so there isn't anything much concrete to work on. And I can function up to a point. People who know me superficially probably wouldn't guess that I'm depressed. I do try and continue doing things. But, so often, there is no real enjoyment. I'm just going through the motions. And I don't know how to change that. I've tried lots of anti-depressants and I've had lots of therapy. I exercise a lot and do other things that are supposed to be mood boosters. I do have good days, but I have many more joyless days. I do think it's important to keep pushing ourselves to do stuff. But I also know how difficult that is. I honestly don't know what else to try, but I'm going to keep trying! Sorry this isn't more helpful! I just wanted to say that I can relate!!
Wishing you all the best (((((((((Shadow Wraith))))))))))