google.com is not listed in the "allow only these domains" list so they cannot access OneDrive files.
partner.com is listed in the "allow only these domains" but OneDrive sharing is set to "existing external users" so a guest user account would be required. Once the guest account is created and the content is shared with the Adatum.com user then the Adatum user will be able to access the content.
https://www.gitbit.org/course/ms-500/learn/Everything-you-need-to-know-about-securing-SharePoint-Online-for-the-MS-500-wv2PbXnhI
https://docs.microsoft.com/en-us/sharepoint/turn-external-sharing-on-or-off