What is the difference between existence/"being" and goodness?

Functional nothing. Both are figments of our imagination. But unicorns and running fountains of chocolate are different. Being is the “con” in consciousness and goodness is the conceit of self-righteousness or the judgement game played on others.

Goodness in the universe is only perceivable from the perspective of a god. And consciousness is just a mirror of the mind of God.

They have nothing to do with one another.

Synonymity? There is no such thing here. These two words mean completely different things.

The difference is that, existence 'is' the definition of a conscious state of being; whereas, goodness is only relative to the perspective of the individual consciousness.
One is a State of Being
The other is the State of Being, of the Being that is.

'Goodness' is the net positive that exists after we recognize all evil and its effects, unmask it from its pretense and demonstrate constructive benefit beyond its momentum of destruction, corruption and detriment.

'Existence' is the state of being itself that contains both good and evil.

Existence relates to mores, relative goodness thereof. Being is of One Mind Soul-realization, of enduring Goodness ("Return to the One: Plotinus's Guide to God-Realization").

Related: "The Path of the Higher Self," "Golden Rules for Everyday Life," "The Great Divorce," "For Couples Only."

They are two different things. Being is the state of existence, or the nature or essence of a living organism, and goodness is one of the (three) modes of material nature by which the material world ( everything and everyone in it) is influenced.

"being" and goodness" existence is simple.
Being is just survival and goodness is trying and help others to have a chance to experience a good life in this tiny world.

Every effect likens to its cause or its first principle. In the case of our creation, our cause is God, the Supreme Good, the Platonic Form of "being" itself.