It is dark circles or spots of any shape on flesh inside, not outside/skin of the stem. When you cut, that cut part should be clear of any spots. Creamy or light green and uniform color. Make sure you sterilize your cutting implement - sharp blade is best: you likely know that, sorry for mentioning it. Outside of the stem/trunk is often marked for different, harmless reasons - what I can see in your photo looks ok to me. Is the stem uniformely firm? Tke photo of the cut for us to see...

@rina The outside is firm, but those dark spots around the inside are giving me deja vu. That Kalanchoe I photographed and you saw a moment ago was just like this, and those dark area inside progressed to rot until I finally cut up high enough to get a 100% clean section.

If any dark cicles, I would keep cutting off in thin slices.

ETA:

checked your other thread; good example of how rot spreads if not gotten rid of completely. Glad to hear that you managed to save some of the cuttings!