First, let's make it clear - there is an automatic way of creating task in Project, when Sales Order is confirmed, so make sure it is not what you need.

If you want to create a Task in specific Project, only if the specific Stage is reached, this is the automation code you want:

project = env['project.project'].search([('name', '=', 'MyProject')], limit=1)

if project:
    new_task = env['project.task'].create({
        'name': 'Task Name',
        'project_id': project.id,
        # Add other fields here
    })
else:
    raise UserError("Project could not be found!")

With this code, on trigger you search for "MyProject" project. If it is found, new task "Task Name" is created in it. If it is not found user gets Error.

Adjust the code to your needs!