This is the default behaviour of FCM. When app is in background it will take white icon. Use this tag and put it in your Manifest. For me this worked. Hope it works for you too[...]

Para resolver você precisa modificar o arquivo ios/Runner.xcodeproj/project.pbxpro e fazer algumas mudanças no Ítem PRODUCT_NAME Substitua o ítem adicionando Runner. Rode novamente: flutter clean && flutter run[...]