For now, there is no such a command line switch.
However, as a workaround, you can enable "Start download without confirmation" setting in Browser Integration options.

I want to download specific URLs (actuary some magnet links) when possible.
Something like RSS but I don't want to download all the links from subscription, and I want to download it only when I want.
Thank you tell me the command line. it is so close to my demand except that I have to check 'OK' in the GUI. Is there any possible I can download a link without check it twice?

Hello,
Unfortunately, the only way for now is to use the command line. And the only argument it supports - is just an URL.
The other APIs are not for public use.
What is your purpose?

on this site I found nothing looks like a document so I put this question here.
There is a remote access in settings but I don't know how to interact with it.