WhatsApp for Nord CE 2

OxygenOS battery restrictions are the usual cause. Go to Settings > Apps > App management > WhatsApp > Battery usage and set it to "Don't restrict". Then open Settings > Battery & device care (Battery) and turn off "Sleep standby optimization" / "Deep optimization" so WhatsApp isn't put to sleep in the background. Confirm WhatsApp has both Mobile data and Wi-Fi enabled under App management > WhatsApp > Data usage, then toggle Airplane mode once or restart the phone to restore the connection. See how others solved this on Reddit

OxygenOS aggressively closes background apps, so first go to Settings > Apps > App management > WhatsApp > Battery usage and choose "Don't restrict", and enable "Allow auto launch" for WhatsApp. Next, in Settings > Notifications & status bar > App notifications > WhatsApp, make sure notifications and the Calls/Messages channels are turned on. Finally, open the Recent Apps screen, pull down on the WhatsApp card and tap the lock icon so the system stops clearing it from memory. See how others solved this on Reddit

The full-screen incoming-call banner needs the "Display over other apps" permission, which OxygenOS sometimes restricts. Go to Settings > Apps > Special app access > Display over other apps and enable it for WhatsApp. Then in Settings > Notifications & status bar > App notifications > WhatsApp > Calls, set the channel importance to high so "Pop on screen" is allowed. With both enabled, the full-screen ringing screen returns instead of just a small heads-up banner. See how others solved this on Reddit

This happens when WhatsApp can't access the camera. First close any other app that may be using the camera, then check Settings > Apps > App management > WhatsApp > Permissions and set Camera to "Allow". If it still fails, clear WhatsApp's cache via App management > WhatsApp > Storage usage > Clear cache and restart the phone. As a workaround, shoot with the stock OnePlus Camera app and attach the photo from your gallery instead. See how others solved this on Reddit

OxygenOS manages cloned apps under App Cloner. Go to Settings > Apps > App Cloner, open WhatsApp and turn the clone off (or choose Delete clone) to remove the second instance. The original WhatsApp and all its chats stay untouched. If you only want it off the home screen, removing the clone here also removes its duplicate icon. See how others solved this on Reddit

App Cloner stores the clone's data under a separate user profile, not the normal WhatsApp folder, so it usually lives at /storage/emulated/999/Android/media/com.whatsapp/WhatsApp/Media (the clone user is typically 999). OxygenOS hides this from the default file picker, so use the OnePlus Files app, enable "Show hidden files", and browse to that path. The most reliable way to move those chats, though, is to back them up from inside the cloned WhatsApp via Settings > Chats > Chat backup to Google Drive. See how others solved this on Reddit