Your soil looks way too dark, rich and water retentive. AND the cactus need more light. That is why it is stretching out. If it is soft, it does sound like rot. You need to up root it and see what is up wittth the roots and see it they are rotted. Then you need to cut all the soft and discolored stuff off . Take a some alcohol and wipe of the knife each time you cut to kill bacteria. Then sprinkle your cut on the cactus with cinnamon (a great natural fungicide) and then let the cactus wounds callus for a week or so.

What do you have your cactus planted in? You need to get a very fast draining mix . Take that mix and dillut it 1 part your soil with 3 parts inorganic grit. It could be pumice, turface, perlite, or a combination . Google Al's gritty mix. Growing cactus is all about the soil.

NOW, how much are you watering? Once you put your cactus in the NEW soil, DO NOT water it till you see roots. Then start very judiciously a little bit at a time . You can mist. Cactus take in moisture through there roots not their stems. They can collect moisture on their needles so a bit of misting is ok. But be judicious and let things dry out well.

Thank you for your help and tips. I will definitely be getting better soil. I am a beginner when it comes to cacti and didn't do my research. That will teach me...

I am only watering when the soil dries out and cracks, but the soil, like you said, is keeping too much water in. I keep the cactus indoors because I like in an apartment and in Minnesota, so it gets cold. Any suggestions about giving it more light?

What is sold as Cactus soil is usually to water retentive and is peat based so needs to be diluted with grit by at least 1part to 1 part. Got any sunny windows or grow lights? I can't help you here, I live in sunny Texas. I am taking my succulents in today since we will be getting the tail end of that "bombogenisis.

Thank you again for your suggestions. I appreciate it a lot. I have a window that gets some sun, but I wish it was more. I may have to look into a light.