What am I doing wrong that my rubber tree has large brown areas on some of its leaves?
Large Brown Areas on Leaves of Rubber Tree
Certified GKH Gardening Expert
There could be several reasons for this and it's often difficult to pinpoint the precise cause. Brown, dead spots on leaves are usually scorching, a sign that your plant is getting too much light. If this is not the case, look towards watering. Brown spots can also be due to a lack of watering. Fungus can be a cause as well, but this is more prevalent in overly moist plants.
Here is an article on caring for rubber tree plants that you may find helpful: https://www.gardeningknowhow.com/houseplants/rubber-tree/how-to-care-for-a-rubber-tree-plant.htm