PPDM and SQL data protection

I assume you've read the ppdm sql guide?
From the "PowerProtect Data Manager 19.21 Microsoft SQL Server User Guide"

"Setting the sysadmin privilege for Microsoft SQL Server hosts

To enable the integration with PowerProtect Data Manager on each Microsoft SQL Server host, ensure that the database OS account or NT AUTHORITY\SYSTEM account on each host has the required sysadmin privilege.
Before you register any Microsoft SQL Server host with PowerProtect Data Manager, set the required sysadmin privilege by completing one of the following two procedures on each Microsoft SQL Server host.

Setting the sysadmin privilege for database OS account

By default, the Microsoft application agent uses the SYSTEM account for asset discovery. However, this requires granting the SYSTEM account the Microsoft SQL Server sysadmin role, which might not comply with corporate security requirements. As an alternative, you can complete the following procedure to use a domain or local user account instead for asset discovery. When you select the option Use the credentials for both asset discovery and backup as follows, the configuration for using the domain or local user account is centrally managed from PowerProtect Data Manager.

Complete the following steps to ensure that the database OS account on each host has the sysadmin privilege.
1. Log in to each Microsoft SQL Server instance, open the SQL Server Management Studio (SSMS), and select View > Object Explorer.
2. In the Object Explorer, expand Security and then expand Logins.
3. Right-click the database OS account name, and then select Properties.
4. In the Login properties window, select Server Roles.
5. Select sysadmin under Server roles.
6. Click OK.
The Login properties window closes.
7. In the PowerProtect Data Manager UI, select Infrastructure > Asset Sources, and then select the SQL tab.
8. Select the required hostname in the list, and then click Edit Credentials.
9. On the Set Credential page, specify the database OS credentials and select the option Use the credentials for both
asset discovery and backup.
NOTE: On the Set Credential page, the option Use the credentials for both asset discovery and backup does not appear when the database OS credentials setting is None.
10. Click Save.

Setting the sysadmin privilege for NT AUTHORITY\SYSTEM account

Complete the following steps to ensure that the NT AUTHORITY\SYSTEM account on each host has the sysadmin privilege.
1. Log in to each Microsoft SQL Server instance, open the SQL Server Management Studio (SSMS), and select View > Object Explorer.
2. In the Object Explorer, expand Security and then expand Logins.
3. Right-click NT AUTHORITY\SYSTEM, and then select Properties.
4. In the Login properties window, select Server Roles.
5. Select sysadmin under Server roles.
6. Click OK.
The Login properties window closes."