FEEDBACK - On MacOS 12.0.1 in UE5 Editor, the shortcut for showing/hiding the Content Browser panel on MacOS is the same as the MacOS system shortcut for Spotlight search - Command + Spacebar (⌘+ [SPACE] )
If it was changed to something else such as Ctl + Spacebar it might work out better for Mac users.
it is ctrl + space, not cmd + space. If ctrl + space is not working, it is probably because of keyboard change shortcut. You can disable it under System Settings > Keyboard > Keyboard Shortcuts > Input Sources > Select the previous input source (Disable or change the binding). Or you can change the shortcut in Unreal Editor by using Preferences menu.