Mac OLM to Gmail Converter
I suggest you use KDETools Mac OLM to Gmail Converter which allows users to save data in various file formats like EML, EMLX, Zimbra, MSG, HTML, etc. The software manages OLM items such as contacts, calendar, emails, tasks, notes and folders, subfolders, etc. The tool allows the user to check the preview of the email with the attachment and full header details. Use the tool to securely import your selected or all of your mailbox items.https://www.kdetools.com/mac/olm/gmail/
If you want to import OLM to Gmail then follow this write-up. Here you get all the methods to import OLM to Gmail with ease. There are two methods available to migrate OLM to Gmail. The first is the manual approach and the second is the use of the Professional solution OLM Converter Tool. The manual approach is quite tricky and requires technical assistance that's why I suggest you to go with the professional solution.
ANKIT ROY commented
As a user, I would like to suggest a professional solution to import OLM into Gmail on Mac. I have used MacSonik OLM Converter Tool for Mac which gave me an effective result for migrating my OLM files into Gmail directly. It is such a hassle-free and most secure process for OLM file conversion. Moreover, we can import bulk OLM files into multiple email clients with the feature of removing duplicate emails. Users can also preview the file before conversion and give the custom name to the resultant file with Mac OLM Converter Tool.
Know more: https://www.macsonik.com/olm/converter/