My recommendation, for what it’s worth, is that you not assume the issue with your dog’s eyes/vision is a cataract until he’s been seen by a vet, preferably an ophthalmologist. Cataracts are fairly common among older dogs, but there are other eye issues that can appear similar but are treated differently.
Here’s an article listing some of the causes of cloudy eyes in dogs. (I’m guessing your boy’s eye is cloudy since you said you can see a cataract forming.)
https://www.petcoach.co/article/7-po...-eyes-in-dogs/
I have a young dog with corneal dystrophy. Just to look at his eyes, most people would guess he has cataracts.