Term that describes one who is an expert in a subject without having any first-hand experience? [duplicate]

This person could be described as an armchair expert, or an armchair X, where X is some occupation (e.g. armchair detective, armchair anthropologist). They may be well-versed in a topic, having studied many books from the comfort of their armchair, but they have little to no practical experience in the field they're studying. They might sound knowledgeable about a subject, but it's entirely possible that their knowledge has little to no bearing on the real world, as it is entirely untested in a practical application.

You're possibly thinking of the Dunning-Kruger effect by which people who lack competence in some area are thus unable to judge their own level of competence and often over-estimate it.

As far as I know, there is no single word for this.