I'm no good at art, so I was looking for something else to do in my free time.
Can we change "no good" into "not good" in the above sentence? Which is more natural? Thanks.
"no good" is more colloquial. It means you're hopeless at it.
"not good" is standard. But you could still be low-average at it and be "not good". "no good" always means "bad".