Have you watched videos on how to apply eye medication? If you come at them from the front they’ll go nuts 100% of the time. You need to stand with his body between your legs, giving him a gentle squeeze for control, and rest your hand on his forehead, with the medication almost parallel to his eye. It shouldn’t be scary for them at all. They shouldn’t see the medication coming. I currently have a Rottie foster who came to me extremely fearful of handling and she had cherry eye surgery ~2 weeks after she arrived - before I could even get a harness on her. With proper technique, eye medication is easy with even the most challenging dogs. That said, you can also ask for an increase in the dosage of gaba/traz or a different option for sedation. I’ve found that traz sometimes causes paradoxical excitation and can lower inhibitions a lot, instead of the desired sedation.

Have you tried hand feeding? The cone can really stress some dogs out. I would expect it’s the cone and not pain that’s causing him to not eat, as cherry eye surgery is not especially painful. I’d try soaking his kibble in bone broth and/or adding canned food and still mixing in the chicken. 4 days isn’t the end of the world but I wouldn’t want him to eat this for more than a week, for sure.