I just tried feeding him again, using the techniques Dakski so kindly shared. I thawed the rat in 90 degree water for two hours and it had thawed to room temperature fully after that. I then used a hair dryer to heat the rat and blast some of its scent towards the enclosure. Originally, he seemed to be interested in wither the smell of the food or the motion of the room. Upon moving the rat into the enclosure and moving it around with my tongs, he seemed to take no notice or care. By this point he was active and moving about his enclosure. Whenever he is awake, he seems super interested in "up." That is to say he explores the lid, stares up into the sky, and otherwise support his body in a vertical fashion. This fasciation kept his mind off the prey as the lid was open and that meant more to explore. (This behavior has persisted since I got him and has not changed with the addition of the CHE or any changes I have made so far.) I quickly hit the rat with a tiny little bit of heat again and left him alone with it for a bit. Again, no interest. At this point I tried dangling and moving the rat about again, but his attention was again elsewhere.

I wonder if humidity has had some effect. I struggle to keep the humidity above 50% after the CHE has been installed. I've been misting twice daily, but it always seems to drop back down to around 50% within a few hours. Foil has not helped much, so I am going to try coconut fiber. Aware that this means another full week of waiting at the least, I plan on making this change sooner than later. At that point I will wash his enclosure as he is due for a sterilization.

I also wonder if scenting the rat with used gerbil bedding might work? I hear they have an attraction to that scent. Additionally, do you think maybe a step down in size is necessary/worth a shot?

It's now been 5 weeks since he has eaten last in the breeder's care. Apollo is not showing extreme weight loss from what I can tell visually. Here is a picture for reference taken after my attempt tonight (the light was turned on after): https://imgur.com/a/e7Tb9NI

Any help or suggestions is once again appreciated.