Hm, that error disappeared, but Software still isn’t displaying any apps. But the updates work now, or at least are displayed, IIRC.
This is the output I get now:
❯ gnome-software
14:24:42:0595 Gs enabled plugins: desktop-categories, fwupd, os-release, shell-extensions, appstream, fedora-pkgdb-collections, desktop-menu-path, epiphany, flatpak, hardcoded-blacklist, hardcoded-featured, hardcoded-popular, modalias, rewrite-resource, rpm-ostree, odrs, provenance, repos, generic-updates, provenance-license, icons, key-colors, key-colors-metadata
14:24:42:0595 Gs disabled plugins: dummy, packagekit, packagekit-local, packagekit-offline, packagekit-proxy, packagekit-refresh, packagekit-upgrade, packagekit-url-to-app, packagekit-refine, packagekit-history, systemd-updates, packagekit-refine-repos
14:24:42:0832 GsPluginRpmOstree can't reliably fixup remote error org.gtk.GDBus.UnmappedGError.Quark._g_2dio_2derror_2dquark.Code0
14:24:43:0081 Gs Only 0 apps for recent list, hiding
14:24:43:0092 GLib g_variant_get_double: assertion 'g_variant_is_of_type (value, G_VARIANT_TYPE_DOUBLE)' failed
14:24:43:0199 Gs not handling error failed for action refresh: Transaction in progress: upgrade
14:24:43:0778 Gs hiding category audio-video featured applications: found only 0 to show, need at least 9
14:24:43:0778 Gs Only 0 apps for popular list, hiding
14:24:43:0778 Gs failed to get featured apps: no apps to show
14:24:43:0778 Gs hiding category games featured applications: found only 0 to show, need at least 9