Using older versions of Outlook for Mac for personal email and calendar
I was added, without my consent to several calendar groups
Spam Group Joins and Calendar Events. Know problem. No fix. All I can offer:
For suggestions on how to Leave a Group. See:
https://learn.microsoft.com/en-us/answers/questions/5915544/no-option-to-delete-calendar-group-in-outlook
Vote for and Comment on this Feature Request:
Add an option to block being added to Outlook Groups without consent
https://feedbackportal.microsoft.com/feedback/idea/a17de24f-8ce6-f011-92b9-7c1e5244b89c
(You must "Sign In" at the top right of the Feedback page before you can vote).