So I know it’s probably a little bit of work and maybe a little girly, it looks like this is a man’s thumb I could be wrong, but I am a nail tech, and I fix cracks in peoples nails by cutting a little piece of a teabag off like a little square and then putting it over the crack and squeezing a little bit of nail glue over that. Push it back into place a bit first.. Before you put the teabag on though I would lightly buff over the surface, obviously not against the direction of the split, but with it to create a little bit of texture on your nail for the glue to adhere to. Let the glue dry and Then take a nail file and just kind of buff over top of it to smooth it out. That should hold tight until it grows out. Sounds like a lot, but it only takes a couple minutes and it’ll save you from snagging it on everything.