Check if you overpotted it. A huge pot makes a cactus focus on roots instead of growing up top. Could also be the opposite, totally rootbound in a tiny container. Either way, the pot size is probably working against you.
True about the pot size thing, but lowkey nobody talks about light direction. If it's only getting strong light from one side, like a window, it'll grow fat and sideways instead of tall. It's reaching, not rising. Might be worth checking if the light source is even all around.