Import objects via Excel overview – Jira Align
There is a section that references XML and XLS and for Mac OS Users only

• For Mac OS users only, when you save the file to import your items back to the system, save the file as a .xml (Excel 2004 XML spreadsheet) file. Then, locate the updated file in your file directory and manually change its extension to .xls. This will format the file so that Jira Align can import it.

But...
Some Windows users are struggling with this as well. I think sometimes Excel changes the extension of the file.

I have just tested the import in Windows and the file needs to be:
Extension: XLS
Format: XML Spreadsheet 2003

Side note:
I found 9ca9aa5ad14e's article here:
https://community.atlassian.com/t5/Jira-Align-questions/Is-there-a-way-to-bulk-edit-update-Capabilities-Epics-in-Jira/qaq-p/1801077?utm_source=atlcomm&utm_medium=email&utm_campaign=immediate_general_question&utm_content=topic
and in step 10, he references changing the extension to XML.

I've reached out to Sam via Slack DM to review this step.