I can't send third party apps like qBittorrent,KeepassXC to system tray instead it gets closed even when the necessary options are marked to use those on background system tray. currently using Elementary OS juno with latest upgrade!
the "problem" is that the Wingpanel-indicator-ayatana is no longer in elementary juno. if you want to install it, try the following link:
sudo apt install software-properties-common sudo add-apt-repository ppa:yunnxx/elementary sudo apt update sudo apt install indicator-application wingpanel-indicator-ayatana sudo nano /etc/xdg/autostart/indicator-application.desktop
change OnlyShowIn=Unity;GNOME; to OnlyShowIn=Unity;GNOME;Pantheon;
Ctrl + O (save change) Ctrl + X (close)
It worked for me.