Thanks Mehjabin Farsana,

I've displayed the aggregated fields by studio > modify the list view > select the quantity column > set the ‘aggregate’ field to ‘sum’.

How can I use them after this ? with developper mode no window is displayed on the aggregated field to find out its name and use it in my field calculation

Hi,
If you've already displayed your aggregated fields but can't use them in your calculated field, it can be due to the fields are not stored properly

Computed fields in Odoo need to be stored in the database if you want to use them in another computed field. Make sure your aggregated fields are set with store=True.

Also make sure that you have added all the required dependencies using @api.depends decorator. If your calculated field depends on the aggregated fields, make sure they are listed in @api.depends.

To know more about this check this video also 

Hope this will help you

Thanks