@Yidi-Huang I have a Pixel 8. I can’t speak for the Outlook issue, but I was seeing similar issues with text messages when I was changing the notification settings for the Messages app. Which Notifications do you have enabled for Messaging (go to Settings -> Notifications -> App notifications -> Messages)? I have everything enabled except for “Messages for web”. With that set, I only see the latest text message from the latest sender and nothing else. I don’t see any previous messages from that sender or any other unread messages. Still annoying that I don’t see all unread messages (I posted a request to fix that https://forum.suunto.com/topic/12016/view-all-unread-text-messages-from-same-sender-thread).
Anyway, when I was fiddling with the notifications I had similar behavior to what you’re seeing. Basically all unread messages would flash across the display of my watch then all I would see would be the oldest unread message. I think that was caused by disabling “Background tasks” from Messages notifications. Take a look and see if that’s the case for you.