Hi @BO ,
Welcome to our forum!
Based on my test in New Outlook for Mac, i found that when we didn't fill in the attendee email address in the "Add required people" field, the "Attendee Options" option was grayed out, as shown in the below image:
Just first enter attendee email address in the "Add required people" field, the "Attendee Options" option will be enabled.
Hope to help you!
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