Q.Ficus tree with brown patches on leaves
We have a ficus tree that we’ve kept in the same pot for a few years. I believe it has not been watered enough, but the leaves are showing more significant problems. Some of the leaves have necrotic, rusty-looking patches near the edges and some leaves have brown patches spreading out over the top side. What is wrong with the leaves and how can we help our tree? I’m attaching a picture. Thank you in advance for your help!

This actually appears to be more of a nutrient issue.
Since the plant has not had new soil for at least 3 years, I would start with that.
New good quality potting mix in a well draining pot, go up only 1 or 2 sizes in pots.
Old soil lack nutrients and salts from watering with conditioned water can build up.
https://www.gardeningknowhow.com/houseplants/ficus/ficus-tree-care.htm
https://www.gardeningknowhow.com/plant-problems/environmental/leaf-chlorosis-and-iron.htm