rspo/default_archiver is a SAP Parameter attribute which is used to control Default device for ArchiveLink requests information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
If no output device is maintained for an archive ID, this parameter is
evaluated to determine a default value. This parameter has the value
ARCH by default. This device is then used to archive.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.