Certified GKH Gardening Expert
I notice a few things. There seems to be some powdery mildew on some of the leaves. This indicates too much moisture or humidity. This will need to be treated with a fungicide. This Brings us to the next thing to consider. ZZ plants thrive on neglect. In fact, over-caring for the plant will usually be the death of it. With this said, they need to be kept away from any direct sunlight, and only watered once the container is completely dry to the bottom. The soil should be rather inert, and feeding should only be done once or twice per year, if it needs. A soil test will confirm whether the soil lacks nutrients or not. Keep in mind that it would rather have less nutrients than more.
This article can help you with your plant's care:
https://www.gardeningknowhow.com/houseplants/zz-plant/caring-for-zz-plant.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
