For starters I have no idea what kind of cactus this is so if anyone can help identify it that'd be awesome. I got it as a tiny little thing from an airport a few years ago and it's done pretty well over the years, up until now.

Recently I noticed it was yellowing at the bottom so I just pulled it up to get a good look at the roots. The soil was dry and loose on top, slightly moist and compacted on the bottom.

I can't tell if this is rot or not.. the discolored portion feels just as firm as the rest of the cactus. No soft spots that I can tell.

I'm not sure if I should just add some rocks to the soil for better drainage and simply repot it, or if I should perform surgery and cut this guy in half. If I cut it..would I cut about at the chopstick level? (See photo)
Never done that before so no idea how it works. Or where roots regrow from. (I know roots grow from nodes on my other houseplants, but no idea with the cactus.)

Any suggestions/advice welcome!! Thank you!

This is an echinocactus grusonii....and ...well there is no sugar coating it no silver lining no dampening this. Really sorry if you find this harsh.
Basically you did a really terrible job at growing it. For starters its conical. For something fat and round to turn into this shape youd have to keep it in the dark for it to etiolate this badly...
Whatever happened to the roots isnt even main problem with this thing basically. Little light means even if you have excellent drainage the plant will simply stay wet.
What I see here is short, bloated roots, which means it may have been growing in unfavorable conditions.
Imma assume you grew this indoors because even in the shade outdoors it wouldnt look this bad.
And this seems to be a long lasting trend. It shouldnt be even this elongated either...barrel cactus and all that.... you may have made it better at one point before getting it even worse...
Cacti in general need lots of light. Indoors, that would be the brightest windows, and preferably outdoors late spring-early autumn. Fast draining soil mainly using coarse, non organic components with some regular added, pot with large drainage holes( plastic ot if yoy can non glazed clay ). Water when dry at the depth(toothpick check). Usually at weekly intervals.

Its basically supposed to look like this(though much smaller, like the tiny branches

Whoa!!! That's what it's supposed to look like?! You're right, I've done an absolute sh** job. I feel terrible lol. I definitely had good intentions when I adopted it, but I think it was only the second plant I'd ever owned and unfortunately I wasn't very attentive to it. (Or my first one, for that matter, which is also in need of some help.) I recently started to take more of an interest in collecting and (properly) caring for plants, so I'm just learning as I'm going.

What can I do now with the one I've got? Is she..doomed? Can I get her healthy again?

aubreyann14 said:Whoa!!! That's what it's supposed to look like?! You're right, I've done an absolute sh** job. I feel terrible lol. I definitely had good intentions when I adopted it, but I think it was only the second plant I'd ever owned and unfortunately I wasn't very attentive to it. (Or my first one, for that matter, which is also in need of some help.) I recently started to take more of an interest in collecting and (properly) caring for plants, so I'm just learning as I'm going.

What can I do now with the one I've got? Is she..doomed? Can I get her healthy again?

Start chopping' from the bottom up and cut until there is no sign of rot in the stem. Then you can wait for it to callus and plant it as a cutting .

sedumzz said:
Start chopping' from the bottom up and cut until there is no sign of rot in the stem. Then you can wait for it to callus and plant it as a cutting .

So it does indeed seem like a case of root rot then? Even though it's not soft/squishy?

Hmm

I was saying to do it if you were sure it was rotten


Don't know if it's rotte. Or not thoguh

I will say if the base is still firm, then you just try to grow it again but watch closely
gradually increase the light exposure.
If you give it enough space and light to grow, it will grow back to a nice round shape. I used to have one cactus ( not sure if it is the same species) that was also elongated but not as bad as yours. After sometime it grows 3 times in volume, into a nice tennis ball shape, you still can see in the picture that the base is very small,

Kaktus said:I will say if the base is still firm, then you just try to grow it again but watch closely
gradually increase the light exposure.
If you give it enough space and light to grow, it will grow back to a nice round shape. I used to have one cactus ( not sure if it is the same species) that was also elongated but not as bad as yours. After sometime it grows 3 times in volume, into a nice tennis ball shape, you still can see in the picture that the base is very small,

An echinopsis. Echinocactus and barrel cacti in general are very hard to rehab like that.