That’s been true for about a year and a half. See the first sentence of the first post in this thread:
on September 15, 2016, an update was released to the android and iOS SmartThings mobile apps which removed the ability to add a new mode through the app. Hopefully this was just a glitch and it will be re-added soon. Meanwhile, you can still add a new mode through the IDE. Instructions in the following thread.
iOS 2.2.0 - Release Notes - #29 by JDRoberts
Follow that link, and it will tell you how to add a new mode through the IDE.
But it’s never been specific to individual devices, just locations ( Hub). You can add a new one or delete an existing one or rename an existing one. But once you’ve given it a name, that’s all there is to it, there are no additional parameters.