Although WhatsApp has supported end-to-end encryption of chats for the several years, this capability does not cover cloud backups, which are uploaded in an unencrypted state. The Facebook-owned chat app clearly notes in its backup settings that "Messages and media backed up in Google Drive are not protected by WhatsApp end-to-end encryption" on WhatsApp for Android.
That said, we know that the company has been testing encrypted cloud backups for well over a year, and after making its way to WhatsApp beta a few months ago, the capability has finally started rolling out generally.
Starting from today, users will have the choice to end-to-end encrypt their backups before they are uploaded to Google Drive or iCloud. WhatsApp has proudly boasted that no other global messaging service of this magnitude provides this capability to its customers.
Despite offering this feature which ensures that neither WhatsApp nor a cloud service provider can read your messages, encrypted chat backups is still an optional layer of security. This is because there are a couple of caveats to be aware of. Backups can be encrypted end-to-end using a password of your choice or a 64-bit key, however, if you lose access to your chats due to some mishap and forget your encryption key too, there is no way to restore the backup. Even WhatsApp won't be able to initiate this process since it claims that it doesn't get access to your key at all.
It appears that this capability is rolling out in a staggered manner since we don't have it on our devices yet. You can head over to Settings > Chats > Chat backup > End-to-end Encrypted Backup to check whether you have the feature yet. You can also utilize our brief guide to configure encrypted cloud backups.