sudo dnf list | grep @rpmfusion-
As far I made the following:
Checking keys with ls /etc/pki/rpm-gpg/ |grep @rpmfusion-
and imported it with rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-rpmfusion-free-fedora-39
Above you find the link to Linux tutorials where I took the info from.
On the top of the Topic I see that you got a message to download the key, did you do that?