WhatsApp for Realme 9

This is almost always ColorOS battery management freezing WhatsApp in the background. Go to Settings > Apps > App management > WhatsApp > Battery usage and set it to 'Allow background activity', and enable 'Allow auto launch'. Then go to Settings > Battery > Sleep standby optimization and turn it off. Finally, open Recent Apps, swipe down on the WhatsApp card (or long-press it) and tap the lock icon so the system stops clearing it from memory. See how others solved this on Reddit

Incoming call alerts need both auto-launch and lock-screen permission, which ColorOS restricts by default. Go to Settings > Apps > App management > WhatsApp and enable 'Allow auto launch', then open Settings > Apps > Special app access > Display over other apps and turn it on for WhatsApp. Finally, in Settings > Notification & status bar > Manage notifications > WhatsApp, open the Calls channel and confirm notifications and 'Lock screen' are both enabled. See how others solved this on Reddit

This is usually the proximity sensor misreading near the earpiece. First clean the top of the screen and any screen protector covering the sensor area, and remove a thick case if you use one. Then disable battery optimization for the app via Settings > Apps > App management > WhatsApp > Battery usage > Allow background activity. If it still happens, clear the app cache under Settings > Apps > App management > WhatsApp > Storage usage > Clear cache, which often fixes the mid-call black screen. See how others solved this on Reddit

ColorOS updates often silently reset per-app background permissions, so WhatsApp gets re-restricted. Re-enable everything under Settings > Apps > App management > WhatsApp: set Battery usage to 'Allow background activity' and turn 'Allow auto launch' back on, then confirm alerts are on in Settings > Notification & status bar > Manage notifications > WhatsApp. If notifications still don't appear, toggle WhatsApp's notification permission off and back on and reboot, which rebuilds the notification channels. See how others solved this on Reddit

If the call alert is suppressed on the phone, it never forwards to a paired watch. On the Realme 9, fully unrestrict both apps in Settings > Apps > App management (set Battery usage to 'Allow background activity' and turn on 'Allow auto launch' for WhatsApp, Signal, and your watch's companion app). Then, in the companion app's notification settings, explicitly add WhatsApp and Signal to the allowed apps so their call alerts relay to the watch. See how others solved this on Reddit