Hi @Beyer, Clay ,
Based on my research, this is not currently possible.
To add a delegate to a private group calendar in O365 SharePoint, the admin needs to be added as a member of the group. This is because only members of the group have access to the group's calendar. Once the admin is a member of the group, they can add events to the group calendar using the "Add Calendar" feature in the directory.
Reference:
Overview of Microsoft 365 Groups for administrators
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