Hi,

To replicate the behavior of the VAT field on a new field created via Studio, you'll need to implement a compute function for your field while ensuring that it has the correct field dependencies.

The VAT field in Odoo typically utilizes a widget called 'field_partner_autocomplete' and may involve a separate module that extends the 'res.partner' model, often named 'partner_autocomplete'. These files can be referenced within the Odoo addons directory to understand better how the VAT functionality is implemented and integrated into the system. Studying these files can provide valuable insights into replicating similar behavior for your custom field.

Hope it helps

I think you will need to add code for that. Try to replicate the behavior using compute fields in Odoo Studio when you add a field and click on `More` you would be able to put the code for the compute field, fields dependencies and everything referring to the others fields in the model or through relationship fields