Probably package issue, i've using Discover with flatpak and flathub configured, also installed applications, that's on 5.20.5. Now (kde-next Discover) flathub did not present in configuration also my applications are gone.
bvbfan Probably package issue
No, issue is in new appstream, known upstream, that is why new appstream did not move out of the build repo.
Just install appstream from the apps repo, until appstream 0.14.0 is replaced. (workaround is to remove the flatpak cache, that will also fix the discover start-up crash).
dconf should be depend in flatpak, now Discover refuses to start, probably some configuration in flatpak is required.