You have new BLS-compatible grubby installed, but BLS feature disabled in grub config. I second @vgaetera, enable BLS
GRUB_ENABLE_BLSCFG=true
then regenerate grub.cfg and either wait for kernel to update to verify grub menu updating correctly – or just manually remove oldest kernel.
The second option – which I don’t recommend – would be to install grubby-legacy (and remove grubby?), legacy is old variant which isn’t BLS-aware and works without it. But again, I don’t recommend going this route, I can see absolutely no reason to do so, and you’d end up with non-standard configuration (which can confuse you in the future).