Hi,

Please try like this:

result= self.env['account.move'].create({
   'partner_id': self.partner_a.id,
   'move_type': 'out_invoice',
   'invoice_line_ids': [(0, 0, {
       'name': 'test line',
       'price_unit': 66.0,
       'quantity': quantity,
       'discount': 0.0,
       'product_uom_id': product.uom_id.id,
       'product_id': product.id,
   })],
})

Here, it is creating a record inside account.move, where invoice_line_ids is a one2many field in the model account.move and product_id, product_uom_id are many2one fields in the one2many lines(invoice_line_ids).

----------UPDATE--------------

You can do it like this for passing value to task_id in each line,

for rec in self.project_detail_ids:
   # do something
   rec.task_id = task_obj.id

It is iterating through each line in project_line_ids.Where, task_obj is a record from the add task table(which may be taken by doing your logic before passing the value to the task_id field in the particular line).

Regards