Q.potted palm
My patio palm after all day rain now has a black and white fungus, and I see black ants on the leaves. Help!

It looks like you have sooty mold growing on your plant.
Likely caused by scale insects.
Neem Oil is a good treatment for you plant.
Here are some links that will help you.
https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm