Haven't changed the soil (normal + peat) since I got it from the nursery. Used to overwater and exposed it to direct sunlight about a month ago. But have moved it indoors once I learned it got sunburn. Now, I water it once a week.

Is my plant healthy? What are the reasons for the brown/black spots on edges of the leaves? What is the white thing on the stem?

Any suggestions are welcome. Thank you!!