but those are not hosted on flathub. Not sure where but elementary/appcenter-reviews/pulls is related. See all json descriptions for apps there.
Wonder if add remote for those runtimes and sdk is the solution for final user or mirror another flatpak repository is possible or makes any sense from flathub.
The exact question is that we distribute apps in flathub that gets obsolete using former runtime, see:
Should we just remove the app and fragment the flatpak experience (totally ok) or keep apps in flathub and other flatpak repositories (elementary)
flatpak remote-add --if-not-exists --system elementary-appcenter https://flatpak.elementary.io/repo.flatpakrepo
flatpak install akira
Buscando coincidencias…
Found similar ref(s) for ‘akira’ in remote ‘elementary’ (system).
Use this remote? [Y/n]: Y
Found ref ‘app/com.github.akiraux.akira/x86_64/stable’ in remote ‘elementary’ (system).
Use this ref? [Y/n]: Y
Required runtime for com.github.akiraux.akira/x86_64/stable (runtime/io.elementary.Platform/x86_64/6) found in remote elementary
Do you want to install it? [Y/n]: Y