Short answer
Yes, it is safe to give a small amount of plain cooked plantain to a dog even if it has kidney disease or is on medication. Give only small, plain, steamed pieces and avoid any fried or salted versions. Plantain is low in sodium and potassium, so it shouldn't interfere with most meds. Watch your dog for any unusual signs, and call your vet if you notice vomiting, diarrhea, or changes in appetite.
Plantain — Food safety facts
Safe to share · Dogs · full breakdown on the linked food page
Cooked, plain plantain is safe in small pieces. Never fried or salted.
The full verdict, portion guidance and serving notes are collected on the Plantain food facts page.