Is it permissible to consume food products that contain "chicken fat" or "fat" only, knowing that most slaughter in European countries is not halal?

The fat extracted from the suet of slaughtered animals takes the same ruling as the meat. If the meat is permissible (halal (definition)), then the fat is permissible; and if it is forbidden (haram (definition)), then the fat is forbidden. The general rule regarding slaughtered animals in European countries is that they are not slaughtered according to Islamic law (dhakah shar'iyyah) due to the widespread use of electric stunning and similar methods. Therefore, it is not permissible to consume their products as long as one's predominant assumption is that it is forbidden. However, if you are in doubt and your predominant assumption is not that it is forbidden, then the default ruling is permissibility. Nevertheless, piety (wara') dictates avoiding doubtful matters, based on the Prophet's (peace be upon him) saying: "Whoever guards against doubtful matters has indeed acquitted himself with regard to his religion and his honor," and his (peace be upon him) saying: "Leave that which makes you doubt for that which does not make you doubt," especially since they do not refrain from pork and incorporate it into many products.