Hi Dave,
the shortcut entry on that webpage only lists the non-Mac shortcut, which is different on macOS as you found out (it's the standard command+esc value). If that shortcut doesn't work for you please file a bug report, so we can investigate what's wrong.
You can change this shortcut in the xml file which defines the menu. Open the "MySQL Workbench.app" bundle and navigate to the Contents/Resources/data folder. There's a file main_menu.xml. Open that in a text editor and search for "completion". Right below that you see 2 menu entry definitions for "list-members", one for macOS and one for other platforms). They have a "shortcut" entry which you can change. Restart WB to take this change into effect.
Note: command + space is the OS standard for Spotlight. I recommend to use a different shortcut instead.
Mike Lischke, MySQL Developer Tools
Oracle Corporation
MySQL Workbench on Github:
https://github.com/mysql/mysql-workbench
On Twitter:
https://twitter.com/MySQLWorkbench
On Slack: mysqlcommunity.slack.com (#workbench)
Report bugs to
http://bugs.mysql.com
MySQL documentation can be found here:
http://dev.mysql.com/doc/refman/8.0/en/