I have seen differences in this behavior depending on the Emacs build. The emacs-mac port (https://github.com/railwaycat/homebrew-emacsmacport) seems to intercept certain Mac-specific keybindings such as C-space and C-M-space and gives them their "Mac meaning", e.g. to bring up Spotlight or the symbol chooser. I could never figure out how to disable this behavior.

Now I use emacs-plus (https://github.com/d12frosted/homebrew-emacs-plus) and this no longer happens.

--Diego

On Wed, Mar 24, 2021 at 10:34 PM Tim Cross <theophilusx@gmail.com> wrote:

Uwe Brauer <oub@mat.ucm.es> writes:

> Hi
>
> Does anybody know how to achieve the traditional binding of
> C-space to set-mark-command on MacOS (for emacsformacos)?
>
> Shift arrow down works, but will not work for a lot of features in org
> mode.
>

Have you verified c-space is not being used by the macOS UI as a
shortcut for something like spotlight search?

I now use spacemacs, but when I used my own setup, I don't recall having
to do anything special to get this behaviour apart from disabling macOS
shortcuts.

--
Tim Cross