Hi,

Chatter is the means of communication tool located on most of the records in odoo. It lets you email customers immediately from a purchase order, sales order, etc., For example, to discuss details and stay in touch. Employees can use internal notes that are not visible to customers to notify one another about progress or problems in the workflow.

For that, you have to inherit 'mail thread'  then in the form view, you have to add

</sheet>

<div class="oe_chatter">

    <field name="message_follower_ids" widget="mail_followers" groups="base.group_user"/>

    <field name="message_ids" widget="mail_thread"/>

</div>

In order to know,how to add chatter in odoo form view, you can refer the link below

How to Add Chatter to the Form View in Odoo 15

Regards