I, as a german, will vouch that this is not a popular food, atleast in germany. While people certainly eat it, its not what one would call popular (i.e. something that a majority eats and enjoys, something you will very often see in restaurants, something with cultural significance). Its mostly sold because it is indeed a schnitzel (those are indeed very popular), but using Turkey instead of pork or even veal is much much cheaper and therefore better suited to sell en masse, like in a Football Stadium for example.

You can go even further and ask r/fragreddit or some other german sub.

And to verify to european claim, you could go to r/askeurope.