I managed to make the system send a message as a notification when some expiration date is close
BUT
I created a server action and an automatic action both in the GUI
I'd like to use xml files to create such actions
Otherwise I have to remember to create them every time I create a new db
I found something but for Odoo 15, I'm on Odoo 14
The creation of server actions and automated actions from XML
are same in Odoo 14.0 or 15.0 and you can check the Odoo 14.0 Documentation
Example for server action:
<record id="act_hr_employee_holiday_request" model="ir.actions.server">
<field name="name">Time off Analysis</field>
<field name="model_id" ref="hr_holidays.model_hr_leave_report"/>
<field name="binding_model_id" ref="hr.model_hr_employee"/>
<field name="state">code</field>
<field name="groups_id" eval="[(4, ref('base.group_user'))]"/>
<field name="code">
action = model.action_time_off_analysis()
</field>
</record>