Thank you for reaching out to the Q&A Forum.
Based on your description, I would like to share some information that I hope will be helpful.
Since you are using Classic Outlook for Windows with a business account, here are some recommended solutions you can try:
Rule out "Overlay Mode" (The Visual Check)
You first need to check if the events are physically duplicated or just visually stacked.
In your Calendar view, look at the list of calendars on the left > Uncheck the box next to the Shared Calendar so that only your Personal Calendar is selected. Look at the main calendar view.:
- If the events disappear: They were not actually duplicated. You were in "Overlay Mode" > you can try to check the Shared calendar again, then look for the Left/Right Arrow icon on the tab of the shared calendar (at the top of the grid) to separate them side-by-side.
- If the events remain: These are actual duplicates. You can try to check for Mobile Device Interference.
If you have both your Business email and this Shared Calendar synced to a smartphone, the phone’s operating system often merges them. If you create an event on the shared calendar via your phone, the phone may default to saving it to your "Default" (Personal) calendar.
You can temporarily disable the sync for the Shared Calendar specifically on your mobile device settings > Create a test event on your PC. If it does not duplicate, the issue lies in your mobile device's default calendar settings.
Delegate Settings
If you have permissions to manage this calendar, Outlook may be configured to forward meeting copies to you.
In Classic Outlook, go to File > Account Settings > Delegate Access.
If you see your name or the shared account listed, check the setting for "Send meeting requests and responses to me"(or similar) and ensure that "My delegates only" is not selected.
Check Rules
Go to File > Rules & Alerts and look for any rule involving "Meeting Request" or "Calendar" that might be moving a copy of items from the Shared account to your Personal folder.
I hope this information proves help and look for your update via comment section.
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