In case nobody has found the solution yet, it's the language input switcher. If you go to System Preferences -> Keyboard -> Shortcuts, in the list on the left there should be "Input Sources". The shortcut you need to untick is in there.
If the "Input Sources" isn't shown on the left, then go to System Preferences -> Keyboard -> Input Sources (tab at the top) and add one, any will do. This will make the shortcut appear in the list now.
fearoffish got a reaction from SanityFox in Alfred on macOS Big Sur 11.0 beta