Wordpress plugin - custom calendar?

Question

CMS

Good afternoon!
I am looking for a plugin for Wordpress or a third-party CMS to organize a custom calendar or, in other words, a list of tasks and their implementation.
What functionality is needed.
A registered user enters the site, he has a calendar on which his completed or scheduled tasks are marked.
The user can add a task for a certain number and then mark it as completed or not completed.
This is the main functionality.