qBittorrent Flatpak

Installation

To install, simply click the above Get it on Flathub button and follow the instructions.
In reality, 2 branches are provided:

1. Stable (default)
   This follows the regular stable release of qBittorrent (with GUI).

   • To install:

     flatpak install flathub org.qbittorrent.qBittorrent

   • To run:

     flatpak run org.qbittorrent.qBittorrent

2. Beta
   This follows the latest development of qBittorrent and libtorrent-rasterbar. However, due to laziness it isn't updated regularly.

   • Add flathub-beta repository:

     flatpak remote-add flathub-beta https://flathub.org/beta-repo/flathub-beta.flatpakrepo

   • To install:

     flatpak install flathub-beta org.qbittorrent.qBittorrent

   • To run:

     flatpak run org.qbittorrent.qBittorrent//beta

   • Set stable version as the default when you invoke flatpak run org.qbittorrent.qBittorrent

     sudo flatpak make-current org.qbittorrent.qBittorrent stable

   • Set beta version as the default when you invoke flatpak run org.qbittorrent.qBittorrent

     sudo flatpak make-current org.qbittorrent.qBittorrent beta

Revise Filesystem Permission

In order to secure the installation, you are encouraged to remove the default --filesystem=host permission or reduce it to suit your need.
Ideally, host should not be the default but it cannot be changed now as it will massively disturb a lot of existing users and seeders.
To remove the permission, you can use Flatseal app or use the following command: flatpak override --nofilesystem=host org.qbittorrent.qBittorrent
Note that there are various qBittorrent functionalities and use cases that would be easier to setup when host or some specific filesystem permission is granted. To name a few: Run external program on torrent complete. Migrate away from flatpak qBittorrent to non-flatpak qBittorrent.
Ref: https://docs.flatpak.org/en/latest/sandbox-permissions.html#filesystem-access

Build Locally

1. Add flathub repository to current user:

   flatpak remote-add \
     --if-not-exists \
     --user \
     flathub https://dl.flathub.org/repo/flathub.flatpakrepo

2. Build it:

   flatpak-builder \
     --ccache \
     --force-clean \
     --install \
     --install-deps-from=flathub \
     --repo=repo \
     --sandbox \
     --user \
     _build \
     org.qbittorrent.qBittorrent.yaml

3. Run it:

   flatpak run org.qbittorrent.qBittorrent

4. Remove it:

   flatpak uninstall org.qbittorrent.qBittorrent