qBittorrent official forums

I suggest adding an option to see combined file size when selecting multiple torrents. If I have 50 torrents selected I would like to know how much disk space they are going to take combined. It could easily say x/y terabytes downloaded.

You could open an issue at Github to see if there is more interest in it:
https://github.com/qbittorrent/qBittorrent/issues.