How to Add a Domain for a Field Dynamically Based on Another Field in Odoo15 | Odoo Technical Video

I got this in my bd using odoo 15: "onchange method returned a domain, this is deprecated ".

hello,
i had a problem with that
class parent()
field category_id many2one product.category
field child_ids one2many

class child ()
field parent_id many2one
field product many2one product.template

in xml or py
in need to filter the product to; select product from its category
how to pass domain?