On macOS, Control-Space is the default keyboard shortcut for changing input source (also known as keyboard layout or input method).
I frequently write in different languages (English, Hebrew, Russian), so I use this shortcut all the time.
The Wikidata Query UI uses Control-Space for auto-completion of Wikidata item names. I cannot use this useful shortcut, because macOS overrides it.
I can change this setting in macOS, but I'd rather not change it. This kind of thing should remain default.
The Wikidata Query UI should have a different or an alternative shortcut for auto-completion.