You can convert multiple OLM files to PST in bulk by using a dedicated OLM conversion tool such as SysInfo OLM Converter. It supports adding multiple OLM files at once, making it easier to migrate large amounts of Mac Outlook data to PST without processing each file individually.

To begin, install and launch the SysInfo OLM Converter on Windows. Select the Select Files option to add multiple OLM files, or choose Select Folder if the files are stored in one location. After loading the files, preview the mailbox data and select the required emails, contacts, calendars, notes, or other folders. Click Next, choose PST as the saving format, and apply options such as date filters, duplicate removal, or attachment handling if needed. Finally, select the destination folder and click Convert.

The tool maintains the original folder hierarchy and supports bulk conversion without requiring Outlook for Mac. Its free demo converts up to 50 emails per folder, while the full version supports complete conversion.
read more - https://www.sysinfotools.com/olm-converter.php