https://github.com/flatpak/flatpak/issues/1276 I can't open a file in the following kde runtime based apps: * io.mgba.mGBA (File -> Load ROM) * org.fedoraproject.MediaWriter (Custom image) * org.subsurface_divelog.Subsurface (File -> Open logbook) It works in the following apps: * net.mediaarea.MediaInfo (wxwidgets, gnome runtime) * org.gnome.gedit (gnome runtime) * org.videolan.VLC (freedesktop runtime) * org.musescore.MuseScore (also kde runtime based, but working!) Tested on Ubuntu 17.10 and Fedora 27. I pretty sure, this must be kde runtime specfic, because when I compiled VLC against it instead of the freedesktop runtime, the same problem occurs. (I filed it under "flatpak-platform-plugin", because there is no product "flatpak-kde-runtime".
I think, I found the cause. If you run: $ flatpak run --command=sh org.subsurface_divelog.Subsurface Then inside the sandbox: $ rm /run/run/user/1000/flatpak-info $ subsurface Now the file open dialog pops up again normally. So it seems this is caused by the backport of Qt's upstream flatpak portal support: https://cgit.kde.org/flatpak-kde-runtime.git/commit/?id=d17671207dfb71cce86abf641df34f5edc7dbd2e
Should be fixed with the next KDE runtime update.