I know there are sometimes developer betas that accidentally include pre-production hardware info and strings[0], or features that would have no use outside of rumored products, eg WebXR[1], so they exist in iOS. I imagine a bad merge can get internal features into public builds, but they seem to be incredibly rare.

0: https://www.idropnews.com/news/homepod-setup-process-leaked-...

1: https://igamesnews.com/mobile/ios-15-4-leaks-possible-apple-...