Meaning
A white X inside a green square, the button version of the cross mark. It means cancel, close or no, like the button that shuts a window.
People use it to mark items as not included or to close a topic, often when they want a softer look than the red ❌: “Breakfast ❎ not included, sadly” Because green usually means OK, some readers find it confusing, so ❌ is the safer pick when the meaning must be clear.