Find more information here about the technical requirements.
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.
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.
To embed Jira dates, a Jira Cloud instance is required.
Connecting to Jira Server is currently not supported.