Backups have always been WhatsApp's biggest vulnerability. Here's the thing: the correspondence itself is protected by end-to-end encryption, which does not involve a third party in the dialogue, and therefore protects the interlocutors reliably. In addition, recently WhatsApp encrypts the history of conversations, which is stored locally on the device (in simple terms - the list of chats).
However, the backups, which the messenger automatically and by default creates in Google Drive or iCloud cloud, are not protected by any encryption. WhatsApp explicitly warns about this in the backup section, but the fact remains that cloud copies were a vulnerability of your correspondence, and their safety was entirely on the conscience of Google and Apple.
Now, however, all that has changed. WhatsApp has finally decided to protect cloud backups of chats. Now all users of the latest version of the messenger can enable end-to-end encryption for their backups. As a result, all your correspondence will be protected at all stages: during the conversation, locally on your device, as well as in the cloud storage.
It is worth noting that even Telegram, which positions itself as a secure and reliable messenger, cannot boast of end-to-end encryption of cloud copies of chats. Telegram stores all users' chats on its servers, encrypting them according to its own standard, which a priori cannot be more reliable than end-to-end encryption.
The source notes that the new WhatsApp feature will be introduced gradually. To enable end-to-end encryption of cloud backups, open WhatsApp and go to Settings → Chats → Backup → End-to-end encryption → click Continue and follow the app's prompts to create an encryption key. If you don't have "End-to-end encryption" yet, update your messenger in time and it will appear later.