Grubby is no longer used in F30, with the adoption of the boot loader specification (which puts each kernel’s boot entry into a separate file, rather than munging /boot/grub2/grub.cfg).
You can see the process used to install kernel packages by examining the RPM scripts for the kernel-core package:
$ rpm -q --scripts kernel-core-`uname -r`
postinstall scriptlet (using /bin/sh):
if [ `uname -i` == "x86_64" -o `uname -i` == "i386" ] &&
[ -f /etc/sysconfig/kernel ]; then
/bin/sed -r -i -e 's/^DEFAULTKERNEL=kernel-smp$/DEFAULTKERNEL=kernel/' /etc/sysconfig/kernel || exit $?
fi
preuninstall scriptlet (using /bin/sh):
/bin/kernel-install remove 5.1.7-300.fc30.x86_64 /lib/modules/5.1.7-300.fc30.x86_64/vmlinuz || exit $?
posttrans scriptlet (using /bin/sh):
/bin/kernel-install add 5.1.7-300.fc30.x86_64 /lib/modules/5.1.7-300.fc30.x86_64/vmlinuz || exit $?
So to install a kernel the “official” way, you’d want to run
/bin/kernel-install add $kernel_release $path_to_kernel