seedlings: no direct sunlight
How to grow yellow dragon fruit from seeds (part 4)
How to Grow Dragon Fruit From Seed
I give my dragon fruit plant approximately 1 inch of water twice per week during the growing season and 1 inch of water once per week during the winter months.
You have to let your soil dry out at springtime until flowers have appeared and opened.
When I do this I give it a deep water until water comes out the drainage holes in the bottom and don’t water it again until the flowers have bloomed.
https://greenthumbplanet.com/grow-dragon-fruit-indoors/