Hi,

Steps:

Go to Settings → Technical → Automation → Automated Actions.

Create a new one:

Model = CRM Lead

Trigger = On Update

Condition = stage_id == 'X'

Action to do: Execute Python Code.

Code:

# This runs in the context of crm.lead record(s)

for lead in records:

    partner = lead.partner_id

    if not partner:

        continue

    # Decide which products to add

    product_ids = []

    if lead.x_my_checkbox:  # your custom field

        product_ids = [env.ref('your_module.product_a').id,

                       env.ref('your_module.product_b').id]

    else:

        product_ids = [env.ref('your_module.product_a').id]

    # Create invoice (draft)

    invoice = env['account.move'].create({

        'move_type': 'out_invoice',

        'partner_id': partner.id,

        'invoice_line_ids': [

            (0, 0, {

                'product_id': pid,

                'quantity': 1,

                'price_unit': env['product.product'].browse(pid).lst_price,

            }) for pid in product_ids

        ]

    })

    # Post and send by email

    invoice.action_post()

    template = env.ref('account.email_template_edi_invoice')

    invoice.message_post_with_template(template.id)

Hope it helps.