Hi,

Set the email template name and subject.
In the "Body HTML" field, you can design your email as needed, including the button. To add a button, you can use HTML and Odoo placeholders for dynamic data.
Here's an example of an HTML button in the email template:

Html;-

<a t-attf-href="/web?#id={{ object.id }}&amp;view_type=form&amp;model=hr.expense"" style="text-align: center;color: #008CBA;background-color: #008CBA;">View Expense</a>

by using the above HTML code you can create a button in the email template

Hope it helps