Hello. When we create Project from template, it creates Project tasks automatically but seems like it is done by Scheduled script. because it shows me this message Is there any method that we can run exactly after those tasks are created please? I tried UE script afterSubmit event but it didn't work

No, this is NS script, native, and you cannot change it. what I usually do is I create a stand alone project, save it, and then populate with everything I need. How do you create projects, what is your source transaction if any?