Hello, spicehead-n4uks, here are the steps to fix it:
1) Turn off the phone and close Outlook.
2) Launch the iCloud for Windows, but not the browser one.
3) Now you see:
calendar and tasks
photos mail, contacts, calendar and tasks
4) You have to uncheck:
mail, contacts, calendar and tasks
5) Now make sure to delete everything, but with copy (find this option)
6) Sign out of iCloud
7) Sign in to iCloud
8) Check mail, contacts, calendar, and tasks and hit apply. This should resync Outlook and cloud
9) Open Outlook
10) Now the issue should be solved after you delete the duplicates
Caution: Make sure you learn more about backups before deleting anything in Microsoft 365.