WhatsApp for Oppo A98

On ColorOS, when the phone is unlocked many calls show only a heads-up banner instead of the full-screen call screen; this is the default behavior. To make calls show full screen, open Settings > Notification & status bar > Manage notifications, tap your calling app (Phone or WhatsApp), and make sure 'Banner' and 'Lock screen' notifications are enabled. Then go to Settings > Battery > App battery management, find the app and choose 'Allow background activity' so the system doesn't restrict it. For WhatsApp, also turn on its 'Use high priority notifications' setting and grant 'Display over other apps' under Settings > Apps > App management > WhatsApp > permissions, so the call UI can appear over whatever is on screen. See how others solved this on Reddit

First check that your finger or a case isn't covering the bottom mic hole next to the USB-C port, and gently clear any dust or lint from it. Make sure the call isn't muted, and turn off any noise-cancellation toggle in the calling app. To tell whether it's a software or hardware issue, record yourself in a voice recorder app and play it back; if that sounds fine, the fault is likely in one app, so clear that app's cache under Settings > Apps > App management > [app] > Storage usage. If recordings also sound muffled, it points to a hardware fault and you should book a service visit. See how others solved this on Reddit

First confirm WhatsApp has camera access in Settings > Apps > App management > WhatsApp > Permissions, then force-stop and reopen the app to release a camera handle another app may be holding. Clear WhatsApp's cache via Settings > Apps > App management > WhatsApp > Storage usage, and reboot the phone, since a frozen or black front-camera feed is often caused by another app keeping the sensor busy. If the selfie camera also fails in the stock Camera app, update ColorOS under Settings > Software update; if it still fails after that, it likely indicates a hardware fault and needs service. See how others solved this on Reddit

ColorOS aggressively closes background apps to save battery, which is the main cause of late notifications. Go to Settings > Battery > App battery management > WhatsApp and set it to 'Allow background activity' (turn off any 'optimize' option), then in Settings > Apps > App management > WhatsApp > Notifications make sure all categories are enabled. Finally, open the Recent Apps screen, swipe down on WhatsApp's card and tap the lock icon so the system stops clearing it from memory. See how others solved this on Reddit

Large originals from the camera are usually the cause. In the stock Camera app settings you can reduce file size by lowering video from 4K to 1080p, and on supported modes choosing a 'High efficiency' (HEIF) photo format instead of standard JPEG. Inside WhatsApp, open Settings > Storage and data > Media upload quality and set it to 'Standard' so shared photos and videos stay smaller, and use 'Manage storage' on the same screen to delete large forwarded files and videos already taking up space. See how others solved this on Reddit