Message icon not showing the number of unopened messages

First, check if you have unread messages. No badges will be displayed if there are no unread messages.

Then check if Badges is enabled in Messages, go to:

Settings > Notifications > Messages. Enable Badges if it is turned off.

Finally. Check if you have enabled Do Not Disturb. By default, Do Not Disturb is set to hide ALL badges when the feature is enabled. You can disable Do Not Disturb in the control center.

• If you have an iPhone with FaceID, pull down the Control Center from the top right corner.
• If you have an iPhone with TouchID, pull up Control Center from the bottom of the screen.

Find the Focus button, just below Screen Rotation Lock and Screen Mirroring, tap in and disable Do Not Disturb. If you have another Focus profile enabled, disable it.