[jwells89]

On Macs (and presumably iOS devices with a keyboard hooked up) it can be produced by pressing ⌥⇧K and will render so long as the receiving text field can render a system font that contains the symbol.

[darby_eight]

Only under the "ABC" text input. Even "ABC - extended" has this shortcut wired for the "circle" diacritic (e.g. " ̊").

[ReleaseCandidat]

And the keyboard layout is one of the supported ones.