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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
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I think you're referring to the "file picker" window. i think qBittorrent is using Dolphin as the file picker and as everyone else commented already you can get the same behavior if you use the "Details" view. Go the settings on Dolphin and tick the Expandable option
Alternatively, you can add the Folder panel (F7) and have the same functionality while having a "Compact" or "Icons" for the files
You mean the content pane? Dolphin should also have this at Settings → Detail view → Expandable folders, though I don't know if what I'm looking at is old. I don't have a KDE system handy.
I believe you can set dolphin to be like this. I have it so I can either double click to go into a folder, or expand it for the tree view.