cannot disable the automatic capitalization of proper nouns

Setting shows up in the search result, however it doesn’t exist.

@portalmaster4901 that search result was a bug: "Noun capitalization" only exists when German or Luxembourgish is enabled (it capitalizes German nouns), so with English the search led to a screen without it. Fixed in 2.2.1, the next App Store update. A switch for names like London or Monday isn't planned for now, because the dictionary only has them capitalized and other keyboards handle it the same way. If you want one lowercase, press backspace right after it gets capitalized and it goes back to what you typed.