Considering a migration to openSUSE Tumbleweed. Running the live KDE, I installed SperkleShare flatpak via Discover.

Starting from terminal with the following command:
/usr/bin/flatpak run --branch=stable --arch=x86_64 --command=sparkleshare org.sparkleshare.SparkleShare --status-icon=gtk

I get the following errors:
06:45:26 Environment | SparkleShare 3.28.0 (Flatpak)
06:45:26 Environment | Git LFS 2.4.0
06:45:26 Environment | Git 2.17.0
06:45:26 Environment | GNOME (Linux 5.6.8.1)
06:45:26 Cmd | gio set "/home/linux/SparkleShare" metadata::custom-icon-name org.sparkleshare.SparkleShare
06:45:27 Environment | GTK+ 3.22.30

(process:3): GLib-GIO-CRITICAL **: 06:45:28.070: g_application_get_is_remote: assertion 'application->priv->is_registered' failed
06:45:28 Environment | Arguments: --status-icon=gtk
06:45:28 Environment | Status Icon: GtkStatusIcon
Gtk-Message: 06:45:28.099: Failed to load module "unity-gtk-module"
No protocol specified

(org.sparkleshare.SparkleShare:3): Gtk-WARNING **: 06:45:28.112: cannot open display: :99.0

This is obviously not the way it should work, but I can't tell if this is only a Live session issue, or happens on an installed OS as well.

The best solution would be packaging it into the official openSUSE repository, without dependency issues.
Otherwise, a solution for the flatpak package would be a great help too.