Hi Yuossef,

class SaleOrderLine(models.Model):
    _inherit = 'sale.order.line'

    sl_no = fields.Integer(string="Sl. No.", compute="_compute_sl_no")

    @api.depends('order_id.order_line', 'order_id.order_line.display_type', 'order_id.order_line.sequence')
    def _compute_sl_no(self):
        for order in self.mapped('order_id'):
            index = 0
            for line in order.order_line:
                if not line.display_type:
                    index += 1
                    line.sl_no = index
                else:
                    line.sl_no = False

Hope this helps.

from odoo import models, fields, api

class SaleOrderLine(models.Model):

    _inherit = 'sale.order.line'

    sequence_number = fields.Char(string='Sequence', compute='_compute_sequence')

    @api.depends('order_id', 'order_id.state')

    def _compute_sequence(self):

        for line in self:

            if line.order_id:

                sequence = line.order_id.sequence_next()

                line.sequence_number = sequence

sequence_number is a computed field that generates the sequence.

order_id.sequence_next() can be used to fetch the next available sequence for the order.

Make sure you also have a sequence defined for the sale.order model or use the built-in ir.sequence model to manage sequence generation. Adjust the logic as needed based on your specific requirements.

Add a new field in so and add the automation action 
i = 1

for line in record.order_line.sorted(key=lambda l: l.sequence):

    if line.display_type not in ('line_section', 'line_note'):

        line.write({'x_studio_so_line_number': i})

        i += 1

and this code for invoce 
i = 1

for line in record.invoice_line_ids.sorted(key=lambda l: l.sequence):

    if line.display_type not in ('line_section', 'line_note'):

        line.write({'x_studio_line': i})

        i += 1