from odoo import models, fields, api

class ResPartner(models.Model):

    _inherit = 'res.partner'

    unique_id = fields.Char(string='Unique Id', help="The Unique Sequence no", readonly=True, default='/')

    @api.model_create_multi

    def create(self, values):

        res = super(ResPartner, self).create(values)

        company_seq = self.env.company

        if res.unique_id == '/':

            if company_seq.next_code:

                if company_seq.next_code

                    company_seq.write({'next_code': company_seq.next_code + 10000})

                res.unique_id =  "{}{}".format(company_seq.id,company_seq.next_code + 1)

                res.name = "[{}{}]{}".format(company_seq.id,company_seq.next_code + 1,str(res.name))

                company_seq.write({'next_code': company_seq.next_code + 1})

            else:

                res.unique_id =  "{}{}".format(company_seq.id,10000)

                res.name = "[{}{}]{}".format(company_seq.id,10000,str(res.name))

                company_seq.write({'next_code': 10001})

        return res

i found one row bug. Resolved top

Odoo 16 in not working this app. I changed same code lines. I added company id and 10000+ start customer sequence number. New model code bottom

# -*- coding: utf-8 -*-

#############################################################################

#

#    Cybrosys Technologies Pvt. Ltd.

#

#    Copyright (C) 2020-TODAY Cybrosys Technologies()

#    Author: Midilaj ()

#

#    You can modify it under the terms of the GNU LESSER

#    GENERAL PUBLIC LICENSE (LGPL v3), Version 3.

#

#    This program is distributed in the hope that it will be useful,

#    but WITHOUT ANY WARRANTY; without even the implied warranty of

#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

#    GNU LESSER GENERAL PUBLIC LICENSE (LGPL v3) for more details.

#

#    You should have received a copy of the GNU LESSER GENERAL PUBLIC LICENSE

#    (LGPL v3) along with this program.

#    If not, see .

#

#############################################################################

from odoo import models, fields, api

class ResPartner(models.Model):

    _inherit = 'res.partner'

    unique_id = fields.Char(string='Unique Id', help="The Unique Sequence no", readonly=True, default='/')

    @api.model_create_multi

    def create(self, values):

        res = super(ResPartner, self).create(values)

        company_seq = self.env.company

        if res.unique_id == '/':

            if company_seq.next_code:

                if company_seq.next_code

                    company_seq.write({'next_code': company_seq.next_code + 10000})

                res.unique_id =  "{}{}".format(company_seq.id,company_seq.next_code + 1)

                res.name = "[{}{}]{}".format(company_seq.id,10000,str(res.name))

                company_seq.write({'next_code': company_seq.next_code + 1})

            else:

                res.unique_id =  "{}{}".format(company_seq.id,10000)

                res.name = "[{}{}]{}".format(company_seq.id,10000,str(res.name))

                company_seq.write({'next_code': 10001})

        return res