Downloading a WhatsApp backup from Google Drive is a bit different from downloading a regular file like a photo or a PDF. Because WhatsApp backups are and tied to your phone number, Google Drive stores them in a hidden "Manage Apps" section that prevents you from simply clicking a "Download" button.
This is the only official method supported by WhatsApp. It "downloads" your cloud backup and decrypts it directly into the app. How to restore your chat history | WhatsApp Help Center
Instead, you generally "download" the data by through the WhatsApp app itself. If you specifically need to get that data onto a computer, you'll need to use third-party tools or local workarounds. 1. The Standard Way: Restore to an Android Device