In my use case this makes the Filezilla flatpak difficult to use. I have seen a workaround that looks too difficult for most people ([SOLVED] How to open the editor from flatpak version of FileZilla) but quite frankly, not using the Flatpak is easier. So, this is a workaround (For Debian 11 KDE at least) for people with the same problem who don’t want to play with dbus.
- Download Filezilla from the website (Download FileZilla Client).
- Extract it
- Place it somewhere (say ~/.bin/)
- Create a new menu entry pointing to the binary (~/.bin/FileZilla3/bin/filezilla).
Update: Paddylandau has posted his workaround for the Flatpak version of Filezilla on Github.