What a beautiful boy. I love that colour scheme. Looks like a Maran?
I have seen something like this. I hope it's not the same thing. One of my 5yo roos started doing the wobbly feet thing, especially the tapping in one place you can see in the videos, lifting his leg and putting it down real quick while standing in one place, often looking perplexed like he had not meant to do that. It progressed from that to him being unable to keep balance, falling on his side or on his behind and unable to stand, unable to walk upright and doing a kind of half-kneeling walk... at the end he had lost weight, was not cleaning himself, had lost some of his vision and was barely able to walk. That whole process took a year. No vet was able to help. Nothing I gave him helped either. I had to cull him during his 6th year, because it was becoming torture for him. My best guess is that it was some kind of slowly progressing neurological condition, probably genetic. I've never seen that anywhere else. The foot tapping in your video honestly gave me terrible flashbacks. I seriously hope it's not the same thing. Thought I'd share nevertheless.
I would keep giving him vitamins and would recommend Selenium as well, just a tiny bit on the tip of a knife. It helps in some chicken neurological conditions.