Hi,

Create schedule action with the button click function.

<data noupdate="1">

     <record id="ir_cron_scheduler_recurring_action" model="ir.cron">

              <field name="name">Recurring Todo Activity</field>

               <field name="model_id" ref="model_mail_activity"/>

               <field name="state">code</field>

                <field name="code">model.action_done()</field>

                <field name="user_id" ref="base.user_root"/>

                <field name="interval_number">1</field>

                 <field name="interval_type">days</field>

                 <field name="numbercall">-1</field>

     </record>

</data>

Change the interval type as days/months

For creating email template please go through this blog

https://www.cybrosys.com/blog/creating-email-templates-in-odoo-15

Create python function to send email through button function 

def action_done(self):
   mail_template = self.env.ref("module_name.email_template_name")
   mail_template_send_mail(self.id,force_send=True)

Regards