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It looks like bird's nest fungus. This article will help:
https://www.gardeningknowhow.com/ornamental/fungus-lichen/birds-nest-fungus.htm

Here's an article with info:
https://www.gardeningknowhow.com/plant-problems/disease/white-mold-on-plants.htm

It looks like lichens, which are normally harmless. However, they are more often seen on tree bark, but any woody stems can get them. So, something else is killing your plants.

https://www.gardeningknowhow.com/ornamental/fungus-lichen/treatment-tree-lichen.htm
https://extension.psu.edu/lichen-in-the-garden

I have never heard it called that, but I guess that could be another way to say it. I wouldn't know any other configuration for the two molecules, other than water... Which is, also, hydrogen oxygen. I would assume that this is what is mean- Peroxide.

Here's an article that explains how to make this yourself:
https://www.gardeningknowhow.com/garden-how-to/info/diy-bordeaux-fungicide.htm

I'm adding another article that may be helpful: https://www.gardeningknowhow.com/edible/fruits/fegen/winterizing-fruit-trees.htm

No. Use slaked lime or hydrate of lime (calcium hydroxide) which comes in a white powder. Here is more:

https://www.gardeningknowhow.com/garden-how-to/info/diy-bordeaux-fungicide.htm