Hi @CBS1970 ,
To confirm if your issue is related to your Outlook for Mac client, it is suggested for you to try importing some other smaller size of olm datafiles to your Outlook to check if the import feature could work fine. Also, you could try to copy the same olm datafile to other Outlook for Mac client and see if the issue could be reproduced there.
I tried some search about your issue but have not found any information tells this is a version-related issue. In this old similar thread, @Loyolaarokia provided a workaround that help him solve his issue, please check if this could help make a difference to you: Disk Space error when importing Note: Please make sure you have backed up all you data before any operations.
Any update, please feel free to post back.
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.