In that case, you most likely need to enable the main RPMFusion repos too.
sudo dnf install https://mirrors.rpmfusion.org/free/fedora/rpmfusion-free-release-$(rpm -E %fedora).noarch.rpm https://mirrors.rpmfusion.org/nonfree/fedora/rpmfusion-nonfree-release-$(rpm -E %fedora).noarch.rpm
Then reboot, then install the appstream data:
sudo dnf install rpmfusion-\*-appstream-data