Doesn't work for me. The option is always greyed out, and I don't actually see "Float Selected Note," it is always "Float on top" no matter wether my window is floating or not. But I can see on Google that it is yet another common problem in macOS. I run Sierra.
And I see the same situation on my girlfriends Mac, also with Sierra.
And I see the same situation on my girlfriends Mac, also with Sierra.