Cooked liver — Food safety facts
Feed with care · Dogs · full breakdown on the linked food page
A tiny amount of cooked liver is fine, but liver is extremely high in vitamin A — regular feeding causes vitamin A poisoning (bone problems).
Short answer
A tiny piece of plain cooked liver is fine as an occasional treat, but liver is extremely high in vitamin A. Feeding it regularly — even daily — can cause vitamin A toxicity, which leads to bone deformities and stiffness over weeks to months. Keep it to small, rare portions, and never feed raw liver.