The best way to convert Mac OLM Outlook files to PST or in any other format is through an OLM to PST converter tool. This will help you in converting the files in a faster manner. Moreover, it can convert as well as migrate Mac Outlook to Windows Outlook and save OLM files to PST, Gmail, Yahoo Mail, Office 365, etc.
Benefits-
 No files size limitation in this method.
 Option to split the large OLM files to give more space.
 Prevents data loss and converts corrupt files as well.

Know more info- https://www.vsoftware.org/olm-to-pst-converter.html