I recently bought a rubber plant and repotted it as it was root bound.
I'm noticing the leaves are turning yellow with black brown spots on them. I'm watering fine and gave ample fertilizer.
It's been kept outdoors but in indirect sunlight under shade. It's also sprouting new leaves. Could this be a fungus?
The yellowing and black spots are more likely the plant in its previous condition as pot-bound lacking nutrients for new growth, so it steals required elements from the older leaves to feed the new. The extraction of the required elements deprives the old cells of what is required for regular functioning so they die off in spots. If you see more of the yellowing on the oldest leaves then I would think that the plant will thank you for being in a larger pot with new soil which will give it more access to nutrients to continue growth. When the old leaves become unsightly they can be cut off, or you can wait for them to drop naturally.
Note too that the leaf surfaces of this Ficus are quite tough and waxy, indicating that it is difficult for fungi and diseases to get into the leaf without some damage such as mechanical cutting; so the death of the leaf cells are much more likely something that happened inside the plant than outside.
