Hello Jorge,

        Many2many field is not directly being used in search view. However one other option is available, You should follow that alternate way :-
        For example :-
            1)  If sale order having invoice_ids many2many field.
            2)  First make one invoice_number field in sale order.
            3)  In sale order field invoice_ids objects is account.invoice
                    So call account.invoice create method, you can get Source Document (origin) = SO reference number
            4)  Base on origin you can search sale order id and write that invoice number in sale order's field "invoice_number"
            5)  Then "invoice_number" is use in search view.

    Hope this will help you!
    Thanks.