Problems with Freetube Flatpak [SOLVED]

I’ve reported this to the developer and to Salix Linux and now to Flathub.

I’ve installed Freetube flatpak on Salix Linux 15.0 (a fork of Slackware). Installed correctly, opens correctly, but when it comes to “Settings” - “Data Settings” - “Import Subscriptions” the dialogue buttons there only change shade when mouse clicked, instead of opening to the choice of import criteria which would be expected. Any ideas, please?

Now resolved by Salix developer. He identified that an additional Salix package was needed and then everything was as it should be. Missing package was xdg-desktop-portal-gtk.