To export data from Outlook on Mac, follow these steps to create an Outlook for Mac Data File (.olm):
1. Open Outlook: Launch the Microsoft Outlook application on your Mac.
2. Access the Export Option:
Click on the File menu in the top left corner.
Select Export from the dropdown menu:

If Export is grayed out, change to Legacy Outlook:
Click on Outlook then Legacy Outlook:

After Outlook reloads, the Export option should be available.
3. Select Items to Export:
You can choose specific items or categories to export. To export everything, check all the boxes:

4. Choose a location on your Mac to save the exported file and give it a name, then click Save:

The items are exported to the olm file:

Depending on the size of your data, the export may take a few moments. Once done, you will have an .olm file containing your exported data.
The .olm file can be imported back into another instance of Outlook for Mac or transferred to another computer running Outlook for Mac.
If you need to convert this .olm file to PST format for use in Windows Outlook, you will need to use a third-party OLM to PST converter tool, as Outlook for Mac does not support direct export to PST format.