Hello, you can rather say: "The muffin looks good but I am not sure about the taste"

You can say something like "The muffin looks good, but I'm not sure about how it tastes."

I would say, “the muffin looks good, but I’m not sure about the taste”.

"the appearance of muffin looks good but I am not sure about the taste" so to sum up there are 2 main issues here. 1. You are not using an article for the noun "muffin" and 2. you are using unnecessary repetitive language with "appearance/looks" so we can fix this in a number of ways. A: There appearance of the muffin is good but i am not sure about the taste B: The muffin looks good but i am not sure about the taste I think B sounds more fluent, plus it's a bit simpler so win-win

Appearance and looks have the same meaning, so drop one. It would sound more natural if you dropped "appearance". So you'd say "The muffin looks good, but..." In spoken English, "I am" is usually contracted to "I'm", so the second half of the sentence would be "I'm not sure about the taste." Why did I say "the muffin"? Because you are talking about a specific muffin, so you need the definite article.