WhatsApp for Huawei Mate 20

WhatsApp itself does not need Google Mobile Services to run. The Mate 20 originally shipped with GMS, so if the Play Store works, install WhatsApp from there. If your device has no working Google services (for example after a wipe or on an updated HarmonyOS build), download the official APK from whatsapp.com/android and sideload it. Before installing, allow your browser or file manager to install apps under Settings > Security (Install unknown apps / install external sources). WhatsApp will run normally without Google Play. See how others solved this on Reddit

Use WhatsApp's built-in 'Move to iOS' transfer. Update WhatsApp on the Huawei to the latest version first, then on the new iPhone install Apple's 'Move to iOS' app and start the transfer during iPhone setup. Connect both phones to power and the same Wi-Fi and follow the on-screen prompts. If the transfer fails, fall back to exporting a chat individually from inside the chat via the three-dot menu > More > Export chat, which emails the messages (and optionally media). See how others solved this on Reddit

WhatsApp drops support for old app versions, so an outdated install will stop connecting. Update it via the Play Store, or if Play is unavailable download the current APK from whatsapp.com/android and install over the old one. Also set the clock to automatic under Settings > System & updates > Date & time, since a wrong date or time can block the SMS verification code from being accepted. See how others solved this on Reddit

WhatsApp's cloud backup uses Google Drive, which needs working Google Play services and the Google Drive app both installed and signed into the same Google account. Open WhatsApp > Settings > Chats > Chat backup and confirm a Google account is selected. If the backup hangs, retry on Wi-Fi and clear the cache for Google Play services and Google Drive. If your phone has no working Google services, Google Drive backup won't work at all; use a local backup instead, which WhatsApp writes automatically each night to the WhatsApp/Databases folder in internal storage. See how others solved this on Reddit

If the new phone has Google services, back up in WhatsApp > Settings > Chats > Chat backup, then sign into the same phone number and Google account on the new phone so WhatsApp offers to restore during setup. If the accounts differ or the new phone has no Google services, use a local backup: copy the WhatsApp/Databases folder (and the Media folder) from internal storage to the new phone via USB or a computer, install WhatsApp, then restore the local backup when prompted. See how others solved this on Reddit

This is almost always aggressive battery management closing WhatsApp in the background. Open Settings > Battery > App launch, find WhatsApp, turn off 'Manage automatically' and enable Auto-launch, Secondary launch and Run in background. Then confirm notifications are allowed under Settings > Notifications > WhatsApp, and lock WhatsApp in the recent-apps view so it isn't cleared. The Always On Display only shows simple notification icons, not full WhatsApp content. See how others solved this on Reddit