finally, it was a plugin activation. The plugin was here but not activated. It is a bit disturbing to have a menu entry in the sidebar to access calendar configuration even if plugin is not activated.
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![Elisa [Atlassian]](https://avatar-management--avatars.us-west-2.prod.public.atl-paas.net/initials/ED-1.png "Elisa [Atlassian]"){kind=avatar}
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