Do other users in the organization have the same problem?
What parts of your shared calendar aren't syncing?
How do you share calendars? Please check if your calendar is successfully shared. As far as I know, when a calendar is shared, the recipient will receive an email invitation.
According to my tests on Outlook, if you open a shared calendar via the "Open Shared Calendar" option in Outlook, the calendar will still show up under "Shared Calendar" unless you turn it off manually, but it won't show detailed item information once the user doesn't have detailed item permissions.
If there are no problems with the shared calendar and the steps to open it, try Restarting Outlook after enabling shared calendar improvements to check for any differences.
File >Account Settings >Account Settings>Change.... > More Settings>Advanced > Turn on shared calendar improvements.
Hope this helps!
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