Hi Ahmed Sharief,
Define a custom_field in python file

from odoo import models, fields

class DemoInherited(models.Model):
    _inherit = 'model_name' 

    custom_field = fields.Char(string='Custom Field')

Then check the XML

<!--Inherit the corresponding form view--> 
<record id="view_model_name_custom" model="ir.ui.view"> 
<field name="name">test.custom.form.inherited</field>
     <field name="model">model_name</field> 
     <field name="inherit_id" ref="external_id_of_form"/> 
     <field name="arch" type="xml"> 
          <xpath expr="//field[@name='field_in_original_form']" position="after"> 
               <field name="custom_field"/>
          </xpath> 
     </field> 
</record>

Thank you

Nikhil krishnan

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