Outlook Calendars for Confluence supports to embed Group and Teams channel calendars directly into Confluence. However, due to restrictions in Office 365, accessing Groups and Teams channels requires an admin consent and is not enabled by default.
Working with Groups and Teams channels requires the Office Permission: Group.ReadWrite.All and
Steps to enable Group and Teams channel calendars
📂 Open the following URL, login as Office admin and consent the permission for the organization.
Afterwards every user can open Group and Teams channel calendars on his own.