Calendar not found in my Nextcloud version


I am doing a project for a class and for it I installed Nextcloud on an Ubuntu server using Docker. Since the project it’s based on creating an event, I would like to have a calendar, but I have tried to install it but the app it’s not found. I get the message “No apps found for your version” even though I am using the newest version of Nextcloud.
I am new at this, could someone please help me with my Issue?

Thank you very much!