SUMMARY A Flathub submission request for an Qt application was made recently, and a bug has been found where the application cannot open directories: https://github.com/flathub/flathub/pull/1978 STEPS TO REPRODUCE 1. Run the following commands to install and run the flatpak: flatpak install --user https://dl.flathub.org/build-repo/32694/org.multimc.MultiMC.flatpakref flatpak run org.multimc.MultiMC 2. Try to click either: Folders > View Instance Folder .. or: Folders > View Central Mods Folder OBSERVED RESULT The application window merely hangs when trying to click on either of these menu items. Giving more sandbox permissions for accessing folders, dbus, etc, doesn't make a difference either. EXPECTED RESULT A folder will open in the desktop's file manager. This works as expected with the latest release tarball: https://multimc.org/#Download As well as when compiled from source, as found here: https://github.com/MultiMC/MultiMC5 SOFTWARE/OS VERSIONS Linux distro: Fedora 33 Workstation Desktop: Gnome 3.38.1 Flatpak version: 1.8.3 Flatpak runtime: org.kde.Platform/x86_64/5.15 ADDITIONAL INFORMATION Some debugging has led me to believe that this call to QDesktopServices::openUrl() is the cause of the hanging: https://github.com/MultiMC/MultiMC5/blob/develop/api/gui/DesktopServices.cpp#L84 This bug may also be related to a similar regression fixed in the version of xdg-utils in the Freedesktop runtime: https://github.com/flatpak/flatpak-xdg-utils/pull/36
This behavior is apparently caused by a bug in the application itself. It's been patched and now it works as expected.