My nails stopped growing—is this normal?

I’ve got this weird horizontal line on my big toe. It started out as a thickened ridge in the nail—kind of like a little step—but the color stayed totally normal. Now, the nail has completely stopped growing altogether. Why would that happen?

...honestly, man, you might be starting to grow a hoof or something...😬...

Come on, I'm being serious here—does anyone actually know?

Could this be some kind of fungus? Has anyone else dealt with nail fungus before?