The Log Shipping - Primary Backup Job alarm is raised when the backup job on the primary database is not enabled.
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This alarm alerts you to jobs that are inadvertently or otherwise disabled.

See also the SQL Server | High Availability drilldown | Primaries page | Transaction Log Shipping Primaries grid.

You can configure this alarm to ignore certain values. You can configure different alarm severities for specific primary databases. From the Spotlight Client see Configure | Alarms.