It's been a few years since WhatsApp began encrypting messages sent between users, and recently, the company announced that it would soon add the option to encrypt chat backups stored in the cloud, as well. That feature has been available to beta testers for some time and is now arriving on the public version of WhatsApp worldwide.
The process of backing up chats and media to Google Drive on the app isn't changing, but WhatsApp will now show an additional option of generating a 64-digit encryption key for those backups. The encryption key can be stored locally or wherever the user chooses and can be used to decrypt their Google Drive backup when the need arises. WhatsApp will also provide a cloud-based vault where the encryption key can be stored and secured behind a password.
In addition to making cloud backups more secure, WhatsApp is also working on allowing users to determine the contents of their chat backup so they can make those backups smaller. This particular feature could be in development partly because Google has been getting stingier about the amount of free storage it provides to users across services and could soon start counting WhatsApp backups against a user's storage quota, something that isn't the case right now.
If you use WhatsApp on your Galaxy device, you should be able to update it via the Google Play Store to get access to the new backup encryption feature. An update may not be immediately available, but it should show up in the near future.
