To implement the feature where clicking "Add" opens a popup form, follow these steps:

• Define the Main Model:

Create a model with a One2many field pointing to the related model.

from odoo import models, fields, api

class MainModel(models.Model):
    _name = "main.model"
    _description = "Main Model"
    name = fields.Char(string="Name", required=True)
    related_ids = fields.One2many('related.model', 'main_model_id', string="Related Records")

• Define the Related Model:

Create the related model with a Many2one field pointing back to the main model.

class RelatedModel(models.Model):
    _name = "related.model"
    _description = "Related Model"
    main_model_id = fields.Many2one('main.model', string="Main Model", required=True, ondelete='cascade')
    name = fields.Char(string="Name", required=True)
    description = fields.Text(string="Description")

• Define the Views:

Define the form and tree views for both models. Ensure the One2many field uses the correct widget.

widget="one2many_list"

By following these steps, you will have a popup form to add related records to the main model, similar to the feature in the Odoo survey module.