Hi,
In the employee form, under the HR Settings page, you can see a field named Badge ID, you can record the employee id in this field or generate an id by clicking the Generate Button near this field.

If this doesn't fit perfectly for your need, try displaying the id field in the form and see if it can be used or else, you can add a new field via studio and with a help of an automated action, you can generate a value in the needed format.

Generate Sequential Value using automated action

Thanks

Hello Cruz, 

You can use this third-party application for generating the employee sequence number: https://apps.odoo.com/apps/modules/16.0/dev_employee_number/

thanks