This method will work as long as "DONE" is the same stage in every Project:

1. Create a Server Action that sets the status:

Make a note of the ID of this Server Action (find it in the URL) so you can use it in the View below.  In this example database it was 679.

2. Create a View that inherits the underlying Task List View and adds the button, hiding it when the Task is done:

This gives Users this kind of User Experience: