Enable Visitor Sharing: In the Google Admin console, go to Apps > Google Workspace > Drive and Docs > Sharing settings. Enable the 'Visitor Sharing' feature.
Configure Visitor Sharing: Ensure that the sharing settings allow sharing with external users who do not have a Google account.
Demonstrate to Finance Team: Conduct a training session with the Finance team to demonstrate how to use the Visitor Sharing feature securely.
Share Reports: When sharing the quarterly financial reports, use the Visitor Sharing option to generate a secure sharing link that can be accessed by the external auditor without requiring a Google account.
Monitor and Review: Regularly review shared documents to ensure that access is being appropriately managed and that the security of shared data is maintained.
Reference:
Google Workspace Admin Help - Visitor Sharing
Google Workspace Admin Help - Sharing Settings

Thesecurity health pagein the Google Admin console provides an overview of security settings and highlights potential risks across various services, including Gmail, Drive, and Calendar. This page offers a consolidated view of the security posture of your organization, making it the most efficient option for quickly identifying security risks in preparation for a risk assessment.

https://support.google.com/a/answer/60752?hl=en#:~:text=Approved%20senders%20list%E2%8
0%94,settings%20in%20Google%20Workspace

To receive emails for your domain (terramearth.com) in Google Workspace, you need to add the domain to Google Workspace as either a primary, secondary, or alias domain, depending on your organization's requirements. After adding the domain, you must update the Mail Exchange (MX) records at your domain registrar to point to Google's mail servers. This step is essential to ensure that emails are correctly routed to Google Workspace.

* Access the Transfer Tool:
* In the Google Workspace Admin console, navigate to "Users" > "Transfer tool for unmanaged users".
* Identify Conflict Accounts:
* Use the tool to search for unmanaged users (conflict accounts) that have email addresses matching your company domain.
* Send Transfer Requests:
* Send transfer requests to the identified unmanaged users, asking them to transfer their accounts to your Google Workspace domain.
* Complete the Transfer:
* Guide the users through the transfer process to ensure their accounts are moved to the managed Google Workspace environment.
* Verify the transfer completion and resolve any remaining conflicts.
References
* Google Workspace Admin Help: Transfer tool for unmanaged users