In the Lord of the Rings fandom there’s a persistent debate whether balrogs, or Durin’s Bane specifically, have wings. The text in Fellowship is ambiguous whether what it is describing are literal wings or something else wing-like.

Never knew about this debate, but IMO the text is not ambiguous:

suddenly drew itself up to a great height, and its wings were spread from wall to wall

That’s very literal. Looking into the subject it seems that people think those are metaphorical wings, but I don’t see anything near that phrase that justifies thinking it’s metaphorical.

But also, at the end of the day, it’s a moot debate. Balrogs are Maiar, them having wings or not is as important as the color of the shoes of some other character, they’re spiritual beings that adopt some physical form, which they can change at will.