I downloaded the Cancer King hairstyle and put it into my mod folder. It's not showing up in my game.

The only two options I can think of is that A) this hairstyle somehow won't load because I have MCCC or B) a recent patch, somehow, made the hairstyle unloadable.

I only recently installed Sims 4.

If you recently installed Sims 4, I am assuming you are a new player?

When you are in-game, you must go into game options and enable mods to show up.

Once you tick that box, your mod should show up.

Other reasons mods may not show up:
1.It needs a mesh
2.It is not categorized "feminine" or "masculine" for CAS items, so when you expect to see the guy's hairstyle show up for guys and it doesn't - just "x" the masculine/feminine tags to see the item, but if you have a lot of CC, this can be annoying. Or it could be in the wrong age categories.
3. Build/Buy items not categorized properly.
4. Not in the right folder, or sub-foldered.

I have mods (and script mods, for MCCC) enabled.
I might check the filter. I don't have a whole lot of CC. (in fact, I have little to no CC; I'd say less than 20 items)