OS says No remote refs found:
flatpak install org.telegram.desktop
Looking for matches…
error: No remote refs found similar to ‘org.telegram.desktop’
m@kubuntu:~$ flatpak install org.telegram.desktop
Operating System: Kubuntu 20.04
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.68.0
Qt Version: 5.12.8
Kernel Version: 5.4.0-60-generic
I suppose you have missed flathub installation source from commandline:
flatpak install flathub org.telegram.desktop
The command above will work if you have added this installation source before by running:
Reference: https://flathub.org/apps/details/org.telegram.desktop