WhatsApp for Oppo Reno 11

This is almost always a proximity-sensor issue. ColorOS uses the sensor near the earpiece to detect when the phone is at your ear, and if it is blocked or dirty the call flips to speaker. Wipe the top of the screen by the earpiece and remove any thick screen protector that covers that area. During a call, confirm the earpiece (not speaker) icon is selected on the WhatsApp call screen. To test the sensor, open the Settings search bar, type "proximity" or dial your phone maker's diagnostic test; if the sensor reads as stuck, restarting the phone usually recalibrates it. If it persists across all calls (not just WhatsApp), it points to a hardware sensor fault worth a service-center check. See how others solved this on Reddit

ColorOS aggressively kills background apps to save battery, which silences WhatsApp until you open it. Go to Settings, Battery, App battery management, find WhatsApp and set it to Allow background activity (turn off any power-saving restriction). Then under Settings, Apps, App management, WhatsApp, Notifications, make sure notifications and all categories are enabled. Finally, open Recents, swipe down on the WhatsApp card and tap the lock icon so the system won't clear it from memory. See how others solved this on Reddit

This is a notification-display permission issue in ColorOS. Go to Settings, Apps, App management, WhatsApp, Notifications and enable Allow notifications plus the Calls category. Then in Settings, Notification & status bar, Lock screen notifications, confirm WhatsApp is allowed to show on the lock screen. Also turn off any Do Not Disturb schedule, since it can suppress incoming call banners. Granting WhatsApp Allow background activity (Settings, Battery, App battery management) helps the call ring through reliably. See how others solved this on Reddit

This usually means WhatsApp is being throttled in the background or the app cache is stale. First update WhatsApp from the Play Store, since older builds had a known chat-sorting bug. Then clear the cache via Settings, Apps, App management, WhatsApp, Storage usage, Clear cache (this does not delete your chats). Finally, disable battery restrictions for WhatsApp under Settings, Battery, App battery management by setting it to Allow background activity so new messages sync in real time. See how others solved this on Reddit

WhatsApp needs media permission, and the Media visibility setting controls whether saved files appear in your gallery. Go to Settings, Apps, App management, WhatsApp, Permissions and grant Photos and videos (Files and media). Then in WhatsApp tap the three dots, Settings, Chats, and turn on Media visibility. If thumbnails still show as broken, clear the WhatsApp cache and reopen the chat to force a re-download. See how others solved this on Reddit

This warning appears when WhatsApp detects a modified or unofficial APK, often installed from a non-Play-Store source. First back up your chats via WhatsApp Settings, Chats, Chat backup to Google Drive. Then uninstall the current app and reinstall it only from the Google Play Store (or the official whatsapp.com download) so you get the genuine signed build, and restore your backup when prompted during setup. See how others solved this on Reddit