If you wish to move several tasks from one project to another, you can do this by following the steps below.
Select all of the tasks you wish to move to another project.
A new menu will appear below which allows you to update the status for the selected tasks, add tags, and more.
Click on the three dots on the right side of this menu, and click on Move tasks to project.
Select the Project and Board / Task list to which you want the selected tasks to be moved.