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Slide your ZZ plant gently out of its pot. Loosen the roots so that they are not girdling the root ball and will grow in an outward direction. Release any old soil from the root ball and set it aside briefly.
Mix up a fresh batch of well drained soil for your ZZ plant with three parts good quality potting mix and one part sharp sand or builders sand to increase drainage capabilities. Fill a shallow pot with drainage holes partially full with the new soil mix.
Slide the ZZ plant into the new pot or ground location, gently splaying the roots throughout the soil. Ensure that the soil level stays consistent on the stems of the plant. Fill soil in around the roots, pressing gently with your palm to lightly compact. Water in well til consistently moist but not soaking wet.
https://www.gardeningknowhow.com/houseplants/zz-plant/caring-for-zz-plant.htm

It would be expected to grow anywhere from 2 to 5 feet inches, both in spread and height. This article will help you with the care of these plants: https://www.gardeningknowhow.com/houseplants/zz-plant/caring-for-zz-plant.htm

This appears to have two causes. The plant is getting leggy in response to a lack of light. Even though it can handle lower light, there is a lower limit. This will need just a little more to be happy.

The browning could be something a little more sinister, though.

This is often caused from fungal infections, caused by overwatering. This will need to be fixed with a fungicide. This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

This article will help you with the care of ZZ plants: https://www.gardeningknowhow.com/houseplants/zz-plant/caring-for-zz-plant.htm

There must have been some change in the humidity level, temperature or moisture level of the plant's soil. By correcting the problem, the mold should disappear. If you need some air circulation, put a fan on low nearby. Here are more suggestions:

https://www.gardeningknowhow.com/houseplants/hpgen/preventing-mold-in-the-soil-of-a-houseplant.htm

That looks like a serious fungal infection! Was the soil still wet when you watered it? This will tend to need to dry out pretty well between waterings. This is usually caused by the soil remaining wet for too long. This give the perfect conditions for bacteria and fungus to survive. They are naturally airborne, so you will have to provide an environment that is inhospitable to them. This is pretty far along, but you can attempt to correct the issue.

Mix 1/4 hydrogen peroxide to 3/4 water and water this once. Spray the top with this mixture, and allow to dry again between the next watering. You will only have to do this once, but it may be weeks before you start to see recovery.

https://www.gardeningknowhow.com/houseplants/zz-plant/caring-for-zz-plant.htm

Unfortunately, your photo did not come through. I can't say, with certainty, what your issue is.

My best guess, given the description, is that it is a scale infestation.

This requires manual removal, for the most part, as they seal themselves to your plant. This makes it hard for chemicals to enter their hard shell.

Other methods can work, once you have removed most of them by hand. These articles will help: https://www.gardeningknowhow.com/plant-problems/pests/insects/control-plant-scale.htm

https://www.gardeningknowhow.com/plant-problems/pests/insects/what-is-armored-scale.htm

https://www.gardeningknowhow.com/houseplants/zz-plant/caring-for-zz-plant.htm