MacOS: Russian PC Keyboard Layout Error

A poster the Apple Support Communities has pointed out that the Russian PC keyboard layout supplied with MacOS and iOS has an error: The key which is supposed to produce Ё (U+0401, Cyrillic Capital Letter IO) actually produces Ë (U+00CB, Latin Capital Letter E with Diaresis). A custom layout that corrects this for MacOS can be found here. It's not possible yet to make custom hardware layouts for iOS, so the problem cannot be fixed there.