Does anyone know how to make OLM to PST conversion for free?

There are two specific methods to convert OLM  to PST, manual and automated method.

Manual method is a free method so also called as freeware method . Automated method involves proffessional utility such as OLM to PST converter.

Free OLM to PST conversion is primarily achieved through manual workarounds, such as configuring an IMAP email account (like Gmail) to sync Mac Outlook data, or by using the free trial versions of third-party converter tools like:- 

MailVare Free OLM to PST Converter
BetaVare Export OLM to PST
ToolsBaer for OLM to PST Conversion