Hyperthyroidism has become the number one endocrine disease among cats even though it only began in the late 1970s. I'm not a vet, but videos on the channel share what I've learned over the last 10+ years of dealing with our own hyperT cats plus a few thousand in the online groups.
I hope it helps, but keep in mind that this isn't formal medical advice, just experience (and conversations with some vets as well).
Videos are all free, but your support certainly helps. You can email me for more options if you like.