Disable WhatsApp's cloud backup
WhatsApp takes the backup of every message, video, or photo that is shared on Google Drive or the iCloud. What's worrying is that these backups are not encrypted. Therefore, if you want to ensure privacy, stop uploading data on the cloud.
To disable the cloud backup on Android, click on the three dots given at the top right corner of the app screen. Now tap Settings, go to Chats, go to Chat backup, Back up to Google Drive and then Tap Never.
For iOS, tap 'Settings' at the bottom right corner of the app screen: Tap Chats, then Chat Backup, Auto Backup, Tap Off.
Alternatively, you could also go to iPhone Settings, Tap on your Profile name at the top, iCloud, WhatsApp, Disable