The best way to convert OLM files to PST is by using a converter tool. I will recommend the
MacProTool OLM conveter For Mac. That tool is capable of converting OLM files to PST and multiple different formats such as PST, PDF, MBOX, EML, EMLX, CSV, MSG, GIF, JPG, TIFF, HTML, etc. Import OLM Files to AOL Mail, Hotmail, IMAP, Thunderbird, Zoho Mail, Yandex Mail, and iCloud Mail. It also supports bulk conversion, allows users to preview files before the conversion process, and has no size limitation.