Items are sorted by WBS (like on Gantt Chart)

Can we change the sorting order ?

You can reorder projects in Planning view (Gantt Chart) or Project Portfolio view.
(drag and drop projects)

Hello! I'm having some issues with the display of activities and projects on the timesheet. I have the default project #1 - PROJECT - LEAVE PERIOD, to which the "Ferie" (Holidays) and "Permessi" (Leave) types should be associated. However, these activities appear to be associated with another project, and I'm unable to move them correctly. I am attaching a screenshot. Thank you very much for your response.  

Hello

The projects and activities of the HR module are hidden in the lists.
To add leave in the HR module, you must go to absence types and create your leave from this screen.
The activities will be automatically added to the Leave project of the HR module.

Similarly, these leaves will not be available - read only - in the timesheet, you will have to record the leave in the HR module either on the Absence Calendar screen or on the absence period.
Therefore, it will be impossible for you to move your already existing activities.

Try and execute Consistency fix in Administration page.

Exactly... I believe this is precisely the critical point. After reading this answer, I came across this post regarding the matter: https://www.projeqtor.org/en/kunena-2/5-ask-questions/11527-wbs-numbering?start=6. The technical project "Leave Period" has WBS 1 (not 0), the same as the first project in the list. To solve the issue of sorting in the timesheet, I did the following: I created an administrative project for unplanned absences that can be logged in the timesheet. I moved this project to the top of the view, so it is visually placed right below the "PROJECT LEAVE PERIOD." In this way, I "group" activities related to planned and unplanned absences.