I have had so much experience as a vet tech and out of the hospital with sick animals (all of my non-human kids are problem kids somehow? But I love them)
Any reputable and experienced vet will also refuse to euthanize.
I know I have had to argue that my animal WAS sick and needed care before. I came back from lunch while working vet and the head tech sheepishly told me they DID have to put my dog on oxygen after everyone was commenting how good she looked earlier before a vet check and questioning why I thought she was sick. Sometimes as owners we have that insight. Which is part of my rambling in that other post. There may be something that we're not understanding.... but from our experiences, what we've been told and our lack of having the animal here in person it just sounds like a senior aged animal, not a big issue. It really just sounds like frustrations.
I can't comment about anything like triggers and such, but it definitely sounds like op needs to step back and take a few breaths. It sounds like a lot of circular logic leading to the same stressed decision. Maybe consider a 2nd opinion with another reptile vet. Talk to someone locally with experience with this species. If anxiety or any other type of diversity is there, definitely contemplate is that the reason behind it.
If it really is an issue with not being able to handle an animal of senior age, it may be time to relinquish and stop.
One of the best decisions I had ever seen made at my former hospital was when a client asked for a dog to be put down because she was elderly, had just gotten treated not long ago for a serious illness caused by the dog's separation anxiety/owner's absence on a business trip and the owner was going to be in and out of town for the next few months. We all thought it was sad but agreed the dog would be suffering without the owner and we almost lost her 3x while treating her before. Staff cried. 3 days later, she showed up with a new puppy. We gave the puppy a clean bill of health and told the owner to never come back to our hospital again. Fired her on the spot.
When you reconsider owning an animal because it's older or just not as interesting, that's the sign to Get out for the animal and any future animals sake.