WhatsApp for Samsung Galaxy A7 (2017)

First close WhatsApp, then clear the camera cache under Settings > Apps > Camera > Storage > Clear cache and reboot the phone, since a stuck camera service is the usual cause on this aging A720F. Next open WhatsApp's permissions at Settings > Apps > WhatsApp > Permissions and toggle Camera off and back on so it re-acquires access. If even the stock Camera app fails to launch, that often points to a custom ROM (such as LineageOS) or firmware problem rather than hardware, so try reflashing the official Samsung stock firmware before assuming the sensor is dead. See how others solved this on Reddit

If the phone still powers on, install WhatsApp on your new device, verify the same phone number, and choose Restore when prompted to pull the chats from Google Drive (only if Drive backup was ever enabled on the A7). If the screen is dead but the phone still boots, connect it to a PC and copy the folder Internal storage > Android > media > com.whatsapp > WhatsApp > Databases, which holds the local msgstore backup files. Note that those .crypt backups are encrypted, so they can only be restored on a phone signed into the same Google account and verified with the same number. See how others solved this on Reddit

Yes, it can still run WhatsApp, but first fully charge it and go to Settings > Software update to install any final patches available for this model. Because the A720F's last major version is Android 8 (Oreo) and it no longer receives security updates, keep WhatsApp itself current through the Play Store and avoid sideloading random APKs. For a cleaner start, consider a factory reset under Settings > General management > Reset > Factory data reset before signing back in. See how others solved this on Reddit

WhatsApp still works for now because it continues to support the A7's Android 8 (Oreo) base, even though Samsung stopped shipping firmware updates years ago. Keep the app updated through the Play Store, since WhatsApp periodically raises its minimum Android version and very old devices eventually fall below it. When that happens you'll get an in-app warning, and your options at that point are a newer phone or using WhatsApp Web from a linked computer. See how others solved this on Reddit

Much of that 'Other' bucket is cached media and orphaned WhatsApp files, so start in WhatsApp under Settings > Storage and data > Manage storage to delete large and forwarded items per chat. Then clear the app cache at Settings > Apps > WhatsApp > Storage > Clear cache, and use Settings > Device care > Storage to remove leftover thumbnails and junk. To stop it refilling, turn off auto-saving of incoming media via WhatsApp Settings > Chats > Media visibility. See how others solved this on Reddit

On this older A7 the slowdown is usually the first full backup uploading every photo and video, so connect to strong Wi-Fi and leave it charging overnight instead of backing up over mobile data. In WhatsApp go to Settings > Chats > Chat backup, set 'Back up over' to Wi-Fi only, and turn off 'Include videos' to drastically cut the upload size. If it stalls completely, clear the cache for Google Play services under Settings > Apps > Google Play services > Storage and restart the backup. See how others solved this on Reddit