I figure out temporary solution, is a little bit goofy, but work

def on_close_event(e):
    if e.data == "close":
        print("Saving unfinished tasks...")
        un_tasks = dict()
        i = 0
        for tt in tab_download.tasks.controls:
            if type(tt.value) == str:
                un_tasks[i] = {"ttask": tt.ttask, "value": {"name": "", "path": ""}}
            else:
                un_tasks[i] = {"ttask": tt.ttask, "value": {"name": tt.value.name, "path": tt.value.path}}
            i += 1

        write_unfinished_tasks(un_tasks)
        page.window.prevent_close = False
        page.window.on_event = None
        page.update()
        page.window.close()
        
page.window.prevent_close = True
page.window.on_event = lambda e: on_close_event(e)
page.update()