I’m afraid that Carbide Create doesn’t support that endmill geometry — the underlying CSV does have a corner radius option for it, but CC won’t use it when previewing (it also won’t preview a V endmill when used for other than a V carving).
Enter it as a square endmill and do without the preview of the rounding, or enter it as a ball-nosed endmill, and just remember that more material will be removed for the rounding than is shown.