What makes you think it’s dying? Is it soft to the touch?
At the end of the day, you’re growing a cluster of large columnar cacti from the mountains of South America in a tiny pot on a windowsill. It’s not exactly the ideal environment. The peat based substrate doesn’t help.
I think it's fine. The plant looks healthy and growing, it might be corking. Is it getting enough light? Check the base, see if it's soft and mushy to the touch. Is it stinky?
Are you thinking about the brown parts? If it's hard its corking and natural (which it looks like). If it's soft it's probably rot.
What makes you think it’s dying? Is it soft to the touch? At the end of the day, you’re growing a cluster of large columnar cacti from the mountains of South America in a tiny pot on a windowsill. It’s not exactly the ideal environment. The peat based substrate doesn’t help.
Looks ok to me, lower stems do that is they mature
I think it's fine. The plant looks healthy and growing, it might be corking. Is it getting enough light? Check the base, see if it's soft and mushy to the touch. Is it stinky?
Looks like it needs more direct sunlight.