I can believe that fresh meat saved your cat’s life. Cats are ‘obligate carnivores’ which means their bodies do not produce certain amino acids that can only be found by consuming meat. Putting a cat on a vegan diet is like putting a human on all meat diet. The human will die of scurvy from lack of vitamin C within months.
Veganism is an insane cult, about 80% of vegans have mental issues.
That could be due to vitamin deficiencies.
Vegetarians are also going to be B12 deficient.
Any diet which requires vitamin supplementation to keep you healthy is NOT a good diet to be on.