my Cactus is all mushy and shrunken in at the bottom and I don’t know what’s wrong, or if I can fix it.
I think the problem is too much water, and/or too frequently watered. The cactus will start to rot from roots down upwards. Soil should dry out between waterings. A cactus would normally need water every two weeks. The soil looks very wet, use soil with good drainage capacity, and a pot with drainage holes. I am not sure if this cactus is salvageable, I hope so.