Are products like shampoos or lotions permissible to use when they contain elements such as cetyl alcohol, benzyl alcohol or linalool alcohol?
Yes it is allowed to use shampoos or lotions containing artificial alcohol.
Nothing is Najis unless and until you have concert evidence that it is Najis.
If you have doubt and want to be precautious, it is up to you to do Ehtiyaat (precaution) but we can not call any doubtful item as definitely Najis.
Wassalam.