Please find code in comment :-
Code :-
<record id="crm_lead_view_form_inherit" model="ir.ui.view">
<field name="name">crm.lead.oppor.inherited</field>
<field name="model">crm.lead</field>
<field name="inherit_id" ref="crm.crm_lead_view_form"/>
<field name="arch" type="xml">
<xpath expr="//page[@name='lead']" position="after">
<page name="">
Add your custom fields
</page>
</xpath>
</field>
</record>

thank you, will check this and confirm.

when Upgrading module i am getting error that as below:

<form class="o_lead_opportunity_form" js_class="crm_form">
<header>
<button name="action_set_won_rainbowman" string="Won" type="object" class="oe_highlight" data-hotkey="w" title="Mark as won" attrs="{'invisible': ['|','|', ('active','=',False), ('probability', '=', 100), ('type', '=', 'lead')]}"/>

Field `stage_id` does not exist

View error context:
{'file': 'd:\\program files\\odoo '
'16.0e.20230607\\server\\odoo\\custom_addons\\crm_customz\\views\\crm_leads_custom_inquiry.xml',
'line': 1,
'name': 'crm.leads.inherit',
'view': ir.ui.view(2407,),
'view.model': 'crm.inquiry',
'view.parent': ir.ui.view(2318,),
'xmlid': 'view_crm_lead_form_inherit01'}

My view code as per your advised code:

<?xml version="1.0" encoding="UTF-8"?>
<odoo>
<record id="view_crm_lead_form_inherit01" model="ir.ui.view">
<field name="name">crm.leads.inherit</field>
<field name="model">crm.inquiry</field>
<field name="inherit_id" ref="crm.crm_lead_view_form"/>
<field name="arch" type="xml">
<xpath expr="//page[@name='lead']" position="after">
<page name="">
<group>
<field name="product_id"/>
<field name="qty"/>
</group>
</page>
</xpath>
</field>
</record>
</odoo>

please help.
regards

My Model Code:

from odoo import models, fields

class CRMInquiry(models.Model):
_name = 'crm.inquiry'
_description = 'CRM Lead Inquiry'

product_id = fields.Many2one('product.product', string='Product Name', required=True)
qty = fields.Integer(string='Quantity', default=1)

Hello @SmithJohn45

Hope you are doing well.

As I could see from your code you have created a new model hence you can't inherit another model's view and add the fields there but instead.

You need to add the fields on the same model you want them to be on or use the new model and create a new many2one field on the model related to the new model.

I hope this could help you.