Earlier quoted context omitted.
They say it themselves https://faq.whatsapp.com/android/chats/about-google-drive-ba... "Media and messages you back up aren't protected by WhatsApp end-to-end encryption while in Google Drive."
That statement is correct. E2E encryption is only in effect between two devices communicating with each other. The moment the messages leave the app in any capacity (e.g., screenshots, backup, forwarded to another convo/contact, etc.) it is not longer protected by E2E encryption. The backup file itself that is uploaded to iCloud/GDrive is encrypted; see: https://security.stackexchange.com/questions/136072/how-can-...
https://www.tomshardware.com/news/whatsapp-google-drive-back...