flatpak: cannot add flathub repo on kubuntu 20.04 LTS: TLS support is not available

error: Can't load uri https://flathub.org/repo/flathub.flatpakrepo: TLS support is not available
 

Fix: need to set env. var:

 GIO_MODULE_DIR=/usr/lib/x86_64-linux-gnu/gio/modules/ flatpak -v remote-add --if-not-exists flathub
https://flathub.org/repo/flathub.flatpakrepo