NetWorker SQL backup fails - Cannot log in to SQL Server Default Instance

NetWorker SQL backup fails with this error:
 

Cannot login to SQL Server Default Instance.

Example errors on the SQL Server are:
 

nsrnmsqlra NSR critical Cannot login to SQL Server <SQLName>
nsrnmsqlra NSR critical Microsoft SQL server documentation provides details about the following SQL Server Provider error:
nsrnmsqlra NSR critical Shared Memory Provider: No process is on the other end of the pipe.

nsrsqlsv NSR critical Cannot login to SQL Server Default Instance.
nsrsqlsv: Shared Memory Provider: No process is on the other end of the pipe.
nsrsqlsv: (Error: 233)

See the following Microsoft link.

https://learn.microsoft.com/en-us/sql/tools/configuration-manager/creating-a-valid-connection-string-using-shared-memory-protocol?view=sql-server-ver16
 

Connections to SQL Server from a client running on the same computer use the shared memory and named pipes protocols. 
Shared memory has no configurable properties. Shared memory is always tried first, and can't be moved from the top 
position of the Enabled Protocols list in the Client Protocols Properties list. The Shared Memory protocol can be 
disabled, which is useful when troubleshooting one of the other protocols.

Conclusions

It is necessary to enable Shared Memory on SQL Server in order for NMM to function properly.