I've seen all the Iphone messages, and there are red dots.

All iPhone SMS messages have been read, but there are still red dots for the following reasons:

Unread notifications or new mail: A red dot may indicate that there are still unread notifications, which may come from other applications, such as social media, mail or other messaging applications. Even if all messages in SMS applications have been marked as read, unread notifications from these other applications will still cause red dots.

System cache problem: Sometimes all messages and notifications have been read, and the system still displays red dots due to cache problems. This is due to some errors in the system cache or some applications have not updated their notification status correctly.

Settings problem: Some settings, such as do not disturb mode or mute unknown calls, will cause some notifications to be filtered out and still display red dots.