As you know projects are temporary in nature and have a beginning and end date.
Based on this definition why "Todoist" doesn´t deal with "ends" in all projects we´ve created?
each project can be archived once completed. To do so, simply right-click on it and choose "Archive" from the drop-down menu.
The definition of projects in Todoist can be understood as folders or categories. For example, if you keep private tasks on your list, you can add them in a project called "Home" which won't ever be completed as it would work as a storage for home-based tasks.
If you deal with complex tasks that always require a completion, you could use sub-tasks instead. For example, you can add a customer-specific main task and then attach sub-tasks such as: "review order", "confirm payment", "send invoice" etc. all of which, including the main task, can be completed and all can be stored in a general project called "Work" or "Customers".
To create a sub-task, you can use the arrow buttons on the right side of the task input box or the Ctrl+RightArrow / Ctrl+LeftArrow keyboard shortcuts or, after the task has been added, the drag & drop option in combination with the 1, 2, 3 or 4 number keys on your keyboard (press 1-4 while "holding" a task).
Thank you for your prompted answer!