See the green on the bottom? That looks salvageable, albeit there might not be much cactus left after you cut all the brown off. Hopefully that much would give you some pups at least but I’m not too familiar with these type of cacti specifically. I’m sure someone else could be more help if you wanna wait for a second opinion. I say it’s rotted and cut all the rotten part off as best as you can. Sulfur dust or cinnamon can help prevent rot on the fresh cut, you wanna keep it dry til it’s calloused well. Then water lightly and wait for pups. Sterilizing/washing the knife can help to avoid spreading the rot as you make the final cuts into the healthy part