Let it drop. 和 Let the matter drop. 的差別在哪裡？如果不好說明，請提供一些例句。

Well, in the context that you're asking someone to stop discussing something, " Drop it" is more common.

But to answer your question, 'let it drop' and 'let the matter drop' are the same thing.
'Let the matter drop' is being more detailed than just saying, 'let it drop.'

And while it's fine to say both those sentences, If you want to sound more like a
native, I would just say 'drop it'.