I have many plants inside and outside of the home. Some are doing well. I have lost a few succulents recently. I have a few plants that have whitish, discolored leaves. Could this be a fungus? Could it be what is making some plants not do well? How should I treat this? It doesn't rub off, it is a discoloration.

The elephant ears, and orchid are outside, the palm, pencil cactus cutting and jade plantlet are inside.