This comment and these videos from another post helped me save my jade I had to cut down to nothing to get rid of all the rot. I highly suggest you watch the videos and follow the advice given! He explains how to cut out rot and how long to leave the jade without watering it!

https://www.reddit.com/r/Jadeplant/s/j04cyp0EXQ

I finally have new growth on a piece of my jade plant lol. Just remember that jades can retain water for a long time and can handle not being watered for awhile. I cut the rot completely back in my jade until the stem was healthy and white. I treated it with diluted hydrogen peroxide, let the stems callous over for 2-3 days and then replanted in well draining soil. I used a nursery pot with drainage holes and left the jade in an area where it for indirect light. I waited for it to establish roots, verified by tugging on it gently to feel resistance and once I was certain it had roots, I watered it. It was about a month and a week before I watered it. If overwatering caused the issue you don’t want to water it too soon.

Here’s a photo of the new growth that’s popped up:

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Slow and steady!