WhatsApp for Samsung Galaxy Note 20 Ultra

One UI's aggressive battery management is usually the cause, so go to Settings > Apps > WhatsApp > Battery and set it to Unrestricted, then make sure WhatsApp is not listed under Settings > Battery and device care > Battery > Background usage limits > Sleeping apps (or Deep sleeping apps). Also confirm Settings > Notifications > App notifications > WhatsApp is fully enabled and that WhatsApp's own Settings > Notifications has the right tone and pop-up options turned on. See how others solved this on Reddit

Grant the permission explicitly under Settings > Apps > WhatsApp > Permissions and toggle Microphone on, since a denied or reset permission silences voice and video calls. If it still fails, clear WhatsApp's cache under Settings > Apps > WhatsApp > Storage, reboot the phone, and record a clip in the Voice Recorder app to rule out a hardware mic fault. See how others solved this on Reddit

Stop One UI from killing WhatsApp in the background via Settings > Apps > WhatsApp > Battery set to Unrestricted, and make sure it is not in Settings > Battery and device care > Battery > Background usage limits > Sleeping apps. If the linked session keeps dropping, open WhatsApp > Settings > Linked devices, log out of all sessions, and re-scan the QR code over a stable Wi-Fi connection. With multi-device enabled, linked sessions stay active for a while even when the phone is offline, but the phone should still reconnect to the internet at least every couple of weeks. See how others solved this on Reddit

First back up WhatsApp itself: open WhatsApp > Settings > Chats > Chat backup and run a Google Drive backup using the same Google account you'll use on the new phone, then restore during WhatsApp's first-run setup there. For everything else, use Samsung Smart Switch (Settings > Accounts and backup > Bring data from old device) to transfer apps, photos, and settings via cable or Wi-Fi. See how others solved this on Reddit

This is a known hardware fault with the AMOLED panel, not a WhatsApp or software bug, and it cannot be cleared by clearing app data or factory resetting. Samsung has repaired or replaced affected Note 20 Ultra displays, in some regions even out of warranty as a goodwill measure, so contact Samsung Support or a service centre rather than spending time on app-level fixes. See how others solved this on Reddit

Most Note 20 Ultra owners keep WhatsApp simply because that's where their contacts already are, and the phone runs it without compatibility issues once notifications and battery settings are configured correctly. If you want one inbox for texts, Samsung Messages or Google Messages (with RCS) handles SMS, but neither reaches WhatsApp-only contacts, so running WhatsApp alongside them is the practical setup. See how others solved this on Reddit