iMessage notifications

I have been having a similar problem, no notification tones for iMessages when phones are locked, for a few weeks for my iPhone 12 Pro Max and my wife's iPhone 8 Max, both running IOS 15.4.1. We get tones for SMS, but not iMessage. Message Notifications were always enabled. I tried several fixes found online to no avail. Since the problem was just with iMessage and not SMS, I decided to remove our cell numbers from iMessage and FaceTime and turned both off. We could then receive SMS from other iPhones (and Android phones) with a Notification tone. I then re-enabled our cell numbers/iMessage/FaceTime for our respective phones and now iMessage Notifications are working normally. I am not a programmer, but this appears to suggest a problem with iMessage/iCloud and not the iPhone or IOS, perhaps triggered by IOS updates. I hope this works for you.

Change alert styles

To add or change an alert style for a notification:

1. Go to Settings > Notifications.
2. Select an app under Notification Style. 
3. Choose a type of alert and banner style. 

You can also turn sounds and badges on or off.

Change group notification settings

You can use group notifications or keep them separate.

1. Go to Settings > Notifications.
2. Select an app and tap Notification Grouping.
3. Select one of these options:

• • Automatic: Notifications from each app will appear in groups based on app alerts.
  • By App: All notifications from each app will be grouped into single expandable alerts.
  • Off: Notifications appear in the order they’re received, without grouping.

From here you can also choose how to show notification previews for specific apps. For example, you can have notification previews show up all the time or never, even when your device is locked.