There is a podcast somewhere that the guy ate only meat for a year. He actually did pretty well.
Quite a few people have gone many years carnivore and done quite well - it’s especially good as an elimination diet for folks with autoimmune diseases & those with depression/bi-polar seem to benefit as well. I think Amber O’Hearn, who is well known in the carnivore community, has been carnivore for something like 10 years. Dr. Paul Saladino (carnivore!) has a book coming out in February called The Carnivore Code - here’s his website if you’re interested: https://carnivoremd.com/
Carnivore isn’t for everybody, but when it’s ‘good’ for someone, it seems to be very, very good!