I cannot understand why one of my folders has a text file icon superimposed. I haven’t seen this before.
I suspect the answer is reasonably obvious, and I will accept whatever humiliating sarcasm anyone wishes to deliver.
I have attached a little screen shot for clarity.
Search for “icons” in the Help file (Help > Scrivener Help), and you will find the answer under “The Binder”. In short: it means that the folder has some text in it (i.e. when you toggle off the corkboard, there is some text behind it in the folder document itself).