Oppo
Mark All Messages as Read auf Oppo
Oppo phones running ColorOS ship with Google Messages as the default texting app, not a Coloros-branded one. That matters because the option to clear unread status for every conversation at once lives inside that app's own menu, not in the phone's system settings.
This function is separate from notification settings. It does not silence future texts or delete anything, it only removes the unread marker and the number badge from conversations you have not opened yet.
To mark every conversation as read in one step:
Tap on Messages ➔ Open the Menu ➔ Tap on Mark all as read
The badge on the app icon and the blue dots next to each conversation disappear immediately after this. If only a single conversation stays marked unread afterward, that conversation likely received a new message after you ran the action, so repeat the step.
If you use a different messaging app on your Oppo device, such as a carrier app or another third-party client, this exact path will not apply. Check that app's own menu for a similar bulk option instead.