Verified on Linux Mint 19.2.
Install:
sudo add-apt-repository ppa:qbittorrent-team/qbittorrent-stable
sudo apt update
sudo apt install qbittorrent qbittorrent-nox
qbittorrent-nox --webui-port=9293 -d
Open localhost:9293 in your browser with default user/pwd: admin/adminadmin.
Modify login info in Tools > Options > Web UI > Authentication.
Note:
Without qbittorrent installed beforehand,
you get error Register bittorrent is unset when starting qbittorrent server.