WhatsApp for Samsung Galaxy S8+

The most reliable path on Android is a Google Drive backup. On your old phone open WhatsApp > tap the three dots > Settings > Chats > Chat backup and tap Back Up, making sure it's linked to a Google account you can also sign in to on the S8+. Then install WhatsApp from the Play Store on the S8+, verify the same phone number, and when prompted sign in with that Google account; WhatsApp will detect the backup and offer to restore your chats. Restore only works during this first-time setup, so don't skip it. (Samsung Smart Switch reliably moves apps, photos and contacts, but historically does not transfer WhatsApp message history, so use the Drive backup for your chats.) See how others solved this on Reddit

Yes, the most dependable method on the S8+ is Samsung's Secure Folder. Go to Settings > Biometrics and security > Secure Folder and set it up, then add a second copy of WhatsApp inside the folder and verify it with your second phone number. The app inside Secure Folder runs as a fully separate instance with its own data, so you can keep both accounts logged in side by side. See how others solved this on Reddit

This is almost always Samsung's battery optimization putting WhatsApp to sleep in the background. Go to Settings > Apps > WhatsApp > Battery and set it to Unrestricted, and remove WhatsApp from any "sleeping" or "deep sleeping" apps list under Settings > Device care (Battery and device care) > Battery > Background usage limits. Then confirm Settings > Apps > WhatsApp > Notifications is on, and that in-app WhatsApp Settings > Notifications has sound and high-priority pop-ups enabled. See how others solved this on Reddit

Open WhatsApp > three dots > Settings > Chats > Chat backup, link your Google account, and tap Back Up to send a copy to Google Drive; you can also set a daily, weekly or monthly schedule and choose whether to include videos. WhatsApp also writes a local backup to internal storage every morning (in the WhatsApp Databases folder), which you can copy to a PC as an extra safety net before any reset or transfer. See how others solved this on Reddit

If you never enabled a Google Drive or local backup, the messages lived only in the app's database and there's no official way to bring them back once they're gone. Stop using the phone so you don't overwrite the storage, then check internal storage for any leftover msgstore .db.crypt files in the WhatsApp Databases folder, which you can try restoring on a fresh install using the same phone number. If nothing remains, only a professional data-recovery service has even a slim chance, and success on years-old deleted app data is far from guaranteed. See how others solved this on Reddit

The S8+ is stuck on Android 9 with no more security updates, and WhatsApp periodically raises its minimum supported Android version, so at some point newer releases may stop installing or updating from the Play Store. Avoid modded clients like GBWhatsApp as a workaround, since they risk account bans and have no security backing; keep the official app updated for as long as it's supported. For everyday messaging the phone still works fine, but plan to migrate your number and Drive backup to a newer device before official support ends. See how others solved this on Reddit