Hi Jenan,

You can get the required notification record using the search method by applying the appropriate domain.Since you added compute method for the notification_id field you should iterate the self since there is a possibility of getting multiple objects in self.Then search the corresponding notification for each object in self and assign the value.Also you should assign a value for each record otherwise the compute method will raise an error.So initially you should assign the False value for every record.When you are searching the notification using search method by applying the particular domain there is a chance of getting multiple records, so you should limit the result by one.

Eg:

@api.depends('type_id')
def set_notification_group(self):
   for rec in self:
    rec.notification_id = False
       if rec.type_id.name == "Employee":
           notification = self.env['hr.contract.notification'].search([('name', '=', 'month')], limit=1).id
rec.notification_id = notification.id

Regards