Q.Why Does The Fruit On My Large Dragon Fruit Soft Rot Before Maturing?
My plant shows no signs of fungus otherwise. The fruit starts out green then turns yellow then rots.

Certified GKH Gardening Expert
It could be environmental, such as overwatering, or disease related. These articles should help pinpoint the problem.
https://www.gardeningknowhow.com/ornamental/cacti-succulents/dragon-fruit/dragon-fruit-pests-diseases.htm
https://www.gardeningknowhow.com/ornamental/cacti-succulents/dragon-fruit/how-to-grow-dragon-fruit.htm
https://www.gardeningknowhow.com/ornamental/cacti-succulents/dragon-fruit/no-fruit-on-pitaya-cactus.htm