An outside corner can't have a fillet due to the geometry of the joint. You could do a groove weld if you felt like it, but almost every engineering drawing I've seen will put a double fillet symbol instead of a proper fillet/groove combo.

If you ever want to tear your hair out I've heard welding symbol charts are basically indecipherable to non welder folk. Honestly looks pretty simple to me, but I was raised by a welder, so maybe I've been looking at them longer than most