That's a good sign that it's not a strength issue but an appetite issue. That yogurt has sugar in it which is actually beneficial to him for right now. It will elevate his glucose which feeds all of his systems and will bounce him back onto his scaly little feet more quickly. But sugar beyond that can present a problem for his crop and liver. So that's why the plain Greek yogurt (has live microbes) is better for him.
Make his crumbles available even though he's not craving them at the moment. He'll eat them when he's ready. Meanwhile, any high energy, high protein food will get his systems working again. Offer cooked egg, however he likes egg best, boiled rice, tofu, unsweetened applesauce, raw squash, grated raw carrot. These things will awaken his appetite and give him strength and that will nudge his appetite and get him back to eating normally.
Here's a tip. Get some probiotic tablets, preferably acidolphillus. This will expedite his system returning to normal and greatly improve his poop. It's hard to say whether he had ascites. If he does have it, it's not treatable anyway. It's a symptom of liver disease. It may be this can improve with a little special care. If you can pick up some milk thistle capsules from the vitamin aisle, one capsule a day, whole, directly into his beak can improve liver function.
