Looks like a bit of rot and possibly mould from what I can see. You'd be wise to extract the alkaloids rather than just making a simple brew or consuming cactus powder, which I see from one of your other posts is what you're planning on doing. A little bit of rot might even make the alkaloids more readily available.
I'd also have kept the tips for growing but that's subject to availability of space of course. Would you consider seeing if the largest of the tips will still root? Cactus growing is such a rewarding hobby.
βThere is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
β Jacques Bergier, quoting Fulcanelli