This means that rpmfusion has not yet released new versions for F43 yet. Not a big problem as you can proceed with the F42=>F43 and then check rpmfusion for updates and fix when they become available.
RPMFusion has published repositories for Fedora 43 for a while now, this shouldn’t be a problem. The error message in the post above looks like rpmfusion-free-release is installed but the rpmfusion-free repo is disabled, which could cause this issue.