Yes — cabbage is safe and nutritious, and a whole leaf clipped to the cage makes great shredding enrichment.
Keeper's noteClip a whole leaf to the bars and let your bird shred it. Red cabbage may tint droppings — that's normal.
Why cabbage is good for parrots
Cabbage (green, red, or savoy) is a safe cruciferous green with vitamins C and K and fiber. Red cabbage adds anthocyanin antioxidants. It's low-oxalate, making it a better daily green than spinach or chard.
How to serve it
Wash; offer raw leaves whole or shredded into chop.