OnePlus
Restore Archived Conversations in Messages auf OnePlus
On OnePlus phones running OxygenOS, archiving a conversation moves it out of the main inbox view but keeps every message intact. This is different from deleting a chat, which removes the content permanently. Archived threads stay searchable and can be opened directly from the archive, but they no longer trigger a preview on the Messages start screen, which is why a contact can seem to have vanished.
To bring a conversation back to the main list, open Open the Messages app ➔ Open the menu ➔ Tap on Archived. From the list of archived chats, Tap and hold a conversation to select it, then choose Tap on Restore/unarchive. The thread reappears on the Messages home screen exactly as it was before archiving, including all previous messages and attachments.
Use this restore option whenever you want a chat back in your regular inbox for quick access or new-message alerts. If you only need to check old messages occasionally, you can leave a conversation archived and open it straight from the Archived folder instead. Restoring does not affect notification settings for that contact, so check those separately if alerts still stay quiet after unarchiving.