Hi,

By default in Odoo POS there is only option to provide a global discount to the order as percentage. For that you can go to the Settings of the Point of Sale and under ‘Pricing’ enable ‘Global discounts’. Now you can see two fields, one for ‘Discount product’ and others for ‘Discount %’ Add the discount product and discount percentage, then Save. Now you will have a discount button in the POS screen to add the global discount as percentage.

If you want to add the global discount as amount, you have to use third party applications or customizations.

Regards.