HEIC does not open in most browsers, on many Windows PCs or in a lot of upload forms. CUR is what Windows needs for a custom mouse pointer. HEIC is at home in saving storage on Apple devices; CUR is the usual choice for mouse pointers on Windows. CUR cannot bring back detail that HEIC compression already removed; it simply stores the result without further loss, in a larger file.
The defaults suit most files. Under Options you can pick which icon sizes go into the file.
Most browsers other than Safari cannot read HEIC themselves, so a HEIC decoder of under 1 MB is downloaded the first time and kept in the browser cache. The picture is fitted into squares of the sizes you pick, 32, 48 and 64 pixels by default; the hotspot, the pixel that points, is the top-left corner, where an arrow's tip sits.