<xpath expr="//field[@name='product_id']" position="attributes">
<attribute name="context">{
'partner_id': parent.partner_id,
}
</attribute>
</xpath>

Then after doing this add below code inside product.product model.

@api.model
def _search(self, args, offset=0, limit=None, order=None, count=False, access_rights_uid=None):
product_ids = []
if self._context.get("partner_id") and not self._context.get('product_id'):
partner_id = self.env["res.partner"].browse(self._context["partner_id"])
product_ids = self.with_context(product_id=True).search([('partner_id', '=', partner_id)])
return set(product_ids)
return super()._search(args, offset, limit, order, count, access_rights_uid)