Did you download OneDrive from the Apple's App store? If so it seems like that version does not have the Backup tab. You will need to download the OneDrive installer from Microsoft's website. It is currently located at the following link.
https://www.microsoft.com/en-us/microsoft-365/onedrive/download
From what I get OneDrive needs additional hard drive access permissions which I guess the App store version doesn't allow.