Find more information here about the technical requirements.
Confluence Cloud
There are no specific requirements for Confluence. Outlook Calendars for Confluence works with every plan: free, standard, premium and enterprise.
To edit calendars, a Confluence user is required.
Microsoft 365
Outlook Calendars for Confluence works best with Microsoft 365 business accounts.
Limited functionality for individual calendars can be achieved with Microsoft 365 family and outlook.com accounts. Rooms, groups and shared calendars do not exist in these editions and are not available in Confluence either.
Not supported are all other Microsoft accounts like live.com, hotmail.com etc.
Jira Cloud
To embed Jira dates, a Jira Cloud instance is required.
Connecting to Jira Server is currently not supported.