Freeing up space · Emergency Space
What is the red badge next to the bell on the Home screen?
Short answer: It's the shortcut to Emergency Space, shown only when your built-in drive is at least 95% full — a share of the drive rather than a fixed number of gigabytes.
It's the shortcut to Emergency Space, and it only appears once your built-in drive is at least 95% full. Tap it to open Emergency Space.
It's measured as a share of your drive's size rather than a fixed number of gigabytes, because 25 GB free is comfortable on a 2 TB Mac and nearly fatal on a 256 GB one. A warning that's always on screen stops meaning anything — so when you see this one, it's real. See What is Emergency Space?