When you see that the Texas rainbow cactus begins to turn yellow, know that this can be caused by underwatering or overwatering. When the soil is too wet, then there might be the presence of fungal infections. You should allow everything to dry, and you should not overwater.
Also, the browning and dropping symptoms indicate that your plant is getting too much moisture and water. If there's not enough water, the indication can be seen with the yellow tips that can begin to form on stems and branches.
When you're still in the process of buying the Texas rainbow cactus, make sure to ask first if the soil is properly draining or sandy. When the topsoil does not properly drain, there's a chance that the plant will likely not receive enough water in the future.
Another thing is that the Texas rainbow cactus tends to die when it's constantly getting overwatered and if it's receiving too much rain if planted outside. Use rainwater or distilled water whenever possible as the plants don't like many minerals in their drink.
You can see the squishy stems, drooping growth, and discolored parts that are all signs of too much moisture. It's critical to give the species time to recover and allow the pot to dry. Transfer it to a different container to avoid root rot and prevent it from dripping. If planted outside, you can also transfer it into a pot, especially in the winter, to help it recover.