While FCM messages themselves don't directly control the notification behavior on Android, you're on the right track with options (B) and (C):

(B) Flutter Code: You'll need to use FCM.instance.makeAndroidShowBannerInBackground(true) in your Flutter code to enable banners when the app is in the background.

(C) Custom Message Channels (Recommended): This is the more robust solution. Creating custom message channels with the IMPORTANCE_HIGH setting allows fine-grained control over how notifications appear, even when the app is backgrounded or killed.

Here's why (C) might be preferable:

More Control: Channels offer greater customization for notification appearance and behavior. Future-Proofing: This approach aligns with the latest Android notification practices. https://cafelam.com/elizabeth-fraley-leads-kinderready-to-unleash-real-time-tracking-analytics-to-enhance-childrens-development-and-parental-engagement/