至于【zhìyú】

至于 introduces a new topic at the head of a clause, after another topic has already been talked about. It means "as for": that's settled – now, this.

The topic after 至于 can be a noun or a question-like phrase such as 去不去 or 怎么做. The comment often says the speaker doesn't know, doesn't care, or will deal with it later.

至于 needs something before it

至于 shifts away from a topic already in play. It can't open a conversation or start on the first topic. For "about" or "regarding" with nothing before it, use 关于.

• × 至于这个问题，我想说几句 (opening a talk) → 关于这个问题，我想说几句

至于吗

至于吗 at the end of a sentence is a different use – "is that really necessary?" – and has its own point.