I wonder if RPMFusion kernel modules are signed with Fedora signing key, but if it is true, you have 3 options:
- Wait for RPMFusion to build new kmod- packages. You can't use akmod for a system with Secure boot enabled because, just like dkms, the modules won't be signed and kernel will refuse to load them.
- Disable Secure boot. AFAIK, Fedora should boot without any problems if you disable secure boot after installation (Even if it has, you can enable it again and it must work).
- (Hard way!) Create your own key pairs, enroll it into UEFI, and sign everything (shim, grub2, kernel and all modules) with your own keys!