Hmm, that file didn’t exist. I created it with contents as shown in the doc you linked:
# UPDATEDEFAULT specifies if new-kernel-pkg should make
# new kernels the default
UPDATEDEFAULT=yes
# DEFAULTKERNEL specifies the default kernel package type
DEFAULTKERNEL=kernel-core
I can’t say I remember having to manually create that config file before in the 10 or so years I’ve used Fedora, is it a known recent change?