Q.Polka dot sick
The leaves fell off, but when I pull out the leaves, I find white stuff on all the stems. The fuzz is still there after putting water on them. I don’t know what I can give it.

You may be overwatering your plant.
The soil should be moist but well draining. Make sure the container has a drainage hold; so excess moisture can drain from the soil.
If you are seeing actual mold on the surface or the plant, your plant may not recover.
Remove the dead plant material. Wait to see if any new growth appears.
Here is a link to refresh you on the care requirements.
https://www.gardeningknowhow.com/houseplants/polka-dot-plant/growing-polka-dot-plants.htm