Q.My Cactus Is Going Soft Since Repotting
Repotted my favourite cactus as I’d had it over two years and thought I could do with some more room… that main stem is now soft. HELP

Certified GKH Gardening Expert
That moon cactus grafted to a dragon fruit cactus is suffering from an infection. Likely, this is from soil that remains too moist for too long without a chance to dry out completely. This can happen when attempting to plant a cactus in anything other than a cactus mix. It can happen when a container has no drainage, as well.
Here is an article that will help you to care for the cactus:
https://www.gardeningknowhow.com/ornamental/cacti-succulents/moon-cactus/care-of-moon-cactus.htm