I think I discovered a bug. When I receive a message, I have the option to reply in the popup. If I reply in the popup without opening the messaging app, the notification dot on the messaging app icon will remain, but when you open the messaging app, no chat will be highlighted or indicate that it is unread, however, my reply that I did in the popup will be shown (as if it was already read). The notification dot will remain on the app icon even after closing the messaging app until I actually open the chat that I originally replied to in the pop-up. In the old messaging app, I believe how it worked was when you opened the app, that chat would still be highlighted as unread, even if you had replied in the pop-up. So I think the bug is the chat not remaining highlighted after it's been replied to in a pop-up.
I hope this helps the devs. (I also hope it makes sense, if not I can try to describe it better) Also, not quite sure if I should report this as a bug on the messaging app issue tracker? It could be specific just to my phone. I am on a pixel 8a, updated to 2026100200, and messaging app version 16.