I just want to show the list on the sidebar, not making a new post automatically. Thank you.
I think what you want then is something that can display an RSS feed in your bbPress sidebar. I can’t recall if there is something like that now, for bbPress, but if there is, it would be a plugin.
WordPress has lots of plugins like that, to display RSS content in your WordPress sidebar, maybe something like that could be adapted to bbPress.
There was an old discussion of a bbPress plugin here but I don’t know if that plugin will work any more. Maybe it could be modified, if necessary, to use the latest bbPress.